For the want of a nail the shoe was lost;
For the want of a shoe the horse was lost;
For the want of a horse the battle was lost;
For the failure of battle the kingdom was lost;
And all for the want of a horseshoe nail.
For the want of a shoe the horse was lost;
For the want of a horse the battle was lost;
For the failure of battle the kingdom was lost;
And all for the want of a horseshoe nail.
— "The Horseshoe Nails"
Humanity has come a long way in terms of the complexity of the structures and tools we use. However, increased complexity means more parts to include, and more ways to fail. While it's predictable that trying to operate a machine or populate a building with many of their necessary components or structural supports missing won't end well, sometimes all it takes for a disastrous outcome to occur is to not install. Just. One. Part.
If it wasn't an Act of Sabotage to remove this part, either as a result of not following the building instructions properly or just not finding the part until it's too late, whatever had been built is going to fail because of a single missing element. The same Rule of Funny this trope runs on also dictates disaster probably won't strike until it has been pointed out it should via Puff of Logic or Tempting Fate, and it will probably explode rather than just fall to pieces.
This differs from Didn't Think This Through in that the failure results entirely from the lack of something that was meant to be there in the first place. This seemingly insignificant part is intended to be part of the design, but oopsie, it's not installed...
A character who forgot to install the part can overlap with Spanner in the Works. See also Imperfect Ritual for the magical version, for when a ritual's performance fails due to the absence of a critical component. Compare Carry the One for its mathematical equivalent.
Related to "Could Have Avoided This!" Plot and Now You Tell Me?.
Examples:
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Anime and Manga
- Inverted in a Crayon Shin-chan short; Shin-Chan's father Hiroshi tries fixing a table fan and despite literally ripping out the core, gears, and screws, couldn't get it to work. And then Shin's kid sister Himawari took attention to a particularly shiny piece of bolt, putting it in her mouth and making a run for it, with Hiroshi chasing after her. Shin-Chan promptly reattaches the core and everything, and the fan's suddenly working again while a confused Hiroshi looks at the missing bolt he's holding.
- Fullmetal Alchemist: Winry repairs Ed's automail prosthetic arm by working nonstop for three days straight, not even bothering to sleep, causing her to forget a screw and only notice after Ed is already gone. This unfortunately results in Ed's arm abruptly falling limp just as he encounters the Homunculi in the Fifth Laboratory, allowing Envy to take him out with little issue. However, Ed never learns of Winry's mistake, as she plays along with his assumption that the fight with the Slicer Brothers is what caused the damage.
- In the Grand Finale of Kirby: Right Back at Ya!, the heroes find themselves stranded at Nightmare's base because the Halberd got destroyed, so Meta Knight has everyone use the Monster Delivery system King Dedede uses to teleport themselves to his castle. However, it got heavily damaged during the Destraya invasion earlier, so Professor Curio rushes to repair it, but there's a single screw missing. Luckily, Waddle Doo finds it and the machine delivers the heroes home just in time before Nightmare's base explodes.
- Invoked in Mobile Suit Gundam 00; one of Celestial Being's more guarded secrets is the creation of the GN Drives which give their Gundams their near-unlimited power. So much so that the original creators of the five GN Drives were all killed, the data erased, and their space station destroyed. However, Alejandro Corner is able to find a Haro that contained blueprints to build GN Drives. However, there was one component he couldn't recreate, the TD Blanket, which allows the creation of GN Particles. Thus, the new GN Drive Tau is designed, but without that one piece, the GN Drive Tau is weaker, can't create energy, and, when Trans-Am Mode is implemented in them, it damages or even destroys the GN Drive Tau when activated.
- In the Season 2 premiere of Panty & Stocking with Garterbelt, it follows up the Cliffhanger from the Season 1 finale where Stocking diced Panty into hundreds of cubes. Garterbelt and Briefs scramble to restore Panty once Stocking mutates into a gigantic Ghost monster, but once they do, Panty is inexplicably a Shrinking Violet unwilling to fight. After Panty still grows giant in this state, Briefs gets a Panty Shot and realises why; she’s missing a single piece that happens to be her vagina, prompting everyone to carry the missing piece in a bizarre (and real) Japanese ceremony that ends with Briefs managing to insert the missing piece in, restoring Panty to her brash Super Mode.
- Sherlock Hound: Invoked in "A Small Client," where the engineer Moriarty kidnapped to fix his counterfeiting press reveals he "forgot" a tiny screw that will threaten the whole machine's integrity. He then uses it to bait his guards away so he can escape (it's not clear whether he's bluffing; the press indeed explodes soon after, but Moriarty was already overclocking it).
Fan Works
- Entropy: The Fate of the Hero System: An example where this trope works out in favor of the one responsible; Kota's support items include a pair of gauntlets that can store the water he produces and increase the power and accuracy of his water jets. During the Battle Trials, his opponent Aya uses her Quirk, which allows her to disassemble and reassemble any object with multiple distinct components, to disassemble one of his gauntlets, only to accidentally activate it again and reassemble it - but without one component that's necessary for the gauntlet to handle high water pressure. The gauntlet catastrophically explodes from excessive water pressure the next time Kota tries to use it, costing him the match.
- The Morrigan: As a child, Nika Nanaura killed a corrupt and abusive Dawn of Fold commander by loosening a single bolt in his mobile suit, causing it to tear itself apart from stress. She specifically avoided removing it outright because a loose bolt is an accident, while a removed bolt is sabotage.
Film — Animation
- Aqua Teen Hunger Force Colon Movie Film for Theaters:
- Parodied and subverted; assembling and using Insanoflex exercise machine will reportedly cause the apocalypse, so the Cybernetic Ghost of Christmas Past went back in time and stole a component from the machine's packaging, without which the Insanoflex will simply fall apart. For good measure, the Cybernetic Ghost even projects a hologram of the exercise machine falling to pieces - and for some reason, a hologram of himself humping one of said pieces. However, given that the component is just an ordinary screw, Emory points out that anyone assembling it can just buy a new one, while Oglethorp remarks that they could probably just improvise with a pencil in the screw-hole... and cut to Frylock doing exactly that.
- However, it later turns out that the Insanoflex is also missing a much more important component that it can't even start without, sending Shake, Frylock, and Meatwad on a journey to Dr Weird's lair/loft apartment to get it. Once the component's added - and Carl makes the mistake of actually using the exercise machine - the Insanoflex transforms into a Humongous Mecha and begins rampaging across the city, all while painfully exercising Carl's muscles. However, everything including the missing component is later revealed to be all part of Weird's plan for revenge on Frylock... which is itself part of a plan by Walter Mellon to assassinate both Frylock and Weird.
- LEGO: The Adventures of Clutch Powers: Brick and Bernie are put in charge of building a battle chariot for the team to use to fight Mallock the Malign, the two coming to blows due to Brick wanting to get it done as soon as possible compared to Bernie's slow but organized methods. After Bernie has sorted out the parts, Brick builds the entire chariot while Bernie is reviewing the instruction manual to figure out where to start, with Bernie being impressed by the results until he sees Brick not bothering to read the instructions caused him to leave out an orange gear. After the initial assault on Mallock's castle fails with the gang crashing the chariot during the retreat and everyone trying to shift blame on each other, Bernie tries to put the blame on Brick by insisting the chariot fell apart because he left the gear out.
Film — Live-Action
- Hudson Hawk. The villainous Mayflowers have acquired the gold-making machine of Leonardo da Vinci, which has a critical component made of several parts that fit together. When the Mayflowers force Hudson Hawk to combine the parts, he secretly doesn't include one of the parts. When the incomplete component is used in the machine, it explodes, killing the Mayflowers.
- The Phantom Menace: Anakin Skywalker is preparing his pod racer for an event that will decide whether he remains a slave to Watto or not. Reigning champion Sebulba comes to taunt him, and while there, furtively knocks a piece loose from one engine. During the race, this sabotage nearly causes a catastrophic failure, but Anakin manages to jury-rig a bypass that saves his pod racer.
- The Rocketeer: When Cliff's rocket pack receives a bullet hole, Peevy patches it with a wad of chewing gum. Later, when Cliff has been beaten by Sinclair and is compelled to forfeit the rocket pack, Peevy helps Sinclair put on the device. While doing so, Peevy furtively removes the chewing gum patch over the bullet hole. For a short while, Sinclair is exultant that he can fly around like an evil bird ... until the fuel starts leaking out of the hole, gets ignited by the rocket pack's exhaust, and sets Sinclair alight. Being immolated tends to sour anyone's mood.
Literature
- Fifty Famous People by James Baldwinnote : The Short Story retelling the Battle of Bosworth Field, "The Horseshoe Nails"
, depicts Richard III's farrier running out of nails while shoeing his liege's horse, and choosing to leave nails off, believing he lacks the time to make more. This results in Richard's horse throwing a shoe at a critical moment; he is unhorsed and thereby killed by Henry Tudor's troops. (The story seems to conflate a 13th century German proverb with Richard's "My kingdom for a horse" line in Shakespeare's Richard III. Historical records of the battle argue that Richard's horse actually got stuck in the mud.)
- Reaper Man: Near the end of the book, the New Death possesses Ned Simnel's Combination Harvester and goes after Death... who, prior to this moment, had removed a small part, integral to the machine's frame. Sure enough, it collapses inches before reaching him.
Live-Action TV
- In the ninth episode of Agents of S.H.I.E.L.D., Coulson's team is called in to investigate a recent explosion at an experimental energy plant that took the lives of several workers. While the safety supervisor, Hannah, was originally blamed, it's eventually revealed that Tobias (one of the workers believed to be dead) was responsible. He had a crush on Hannah but couldn't get her attention, so he'd loosen bolts on various parts in his section before reporting the safety issue, giving her a reason to come see him. It was him loosening the wrong bolt on the wrong part at the wrong time that caused the explosion.
- Gekisou Sentai Carranger: In both the original series and the adaptation, Grotch/Porto shows off the Norishiron 12/Terrorzord mecha to Zelmolda/Elgar, but still needs to finish assembling it by adding a last cotter pin. Zelmolda/Elgar swipes the mech and takes off before Grotch/Porto can warn and stop him; consequently, right as the Rangers are on the verge of defeat, the mecha's arm falls off and Zelmolda/Elgar has to retreat without finishing the fight.
- Mayday episode "Breakup over Texas": Some screws were removed for maintenance purposes, but never put back due to bad communication between different groups of people working on the plane. As a result, the leading edge of the stabilizer broke off during a flight, causing the plane to break up in mid-air and everyone on board to die.
- Nikita: A one-off gag in an early episode has Division's trainees learning to field-strip and reassemble firearms. Alpha Bitch Jaden claims to have finished, until the instructor calls attention to several parts she's left on the table. This embarrasses her, especially after her rival Alex does it right on the first try.
- Orphan Black: Echoes: Kira's insurance policy against her organ printer (which can print entire people) being used for nefarious purposes by her wealthy benefactor is to leave a crucial component out of the specs. Only she and one trusted associate know about the missing part. The associate ends up betraying her though, leading to a bunch of undisclosed clones running around.
- Robot Wars:
- When George Francis built the original Chaos for Series 2, he had intended to screw two rounded pieces of polycarbonate onto the back of the machine to help it self-right if flipped over. He forgot to do so, and when Chaos was duly overturned in the heat final against Mace, it was left stranded on its back and counted out.
- Also in Series 2, when Dreadnaut was wheeled into the arena for its heat semi-final match against Oblivion, the team accidentally knocked the safety link out without realising. Without the safety link inserted, Dreadnaut was - by design - completely inoperable, giving Oblivion a free win.
- Star Trek: The Next Generation: In the episode "Starship Mine," Picard is trapped alone on the Enterprise fighting off a group of criminals who are trying to steal highly volatile trilithium resin, while a deadly baryon sweep progresses through the ship. After a scuffle with Picard, the last of the criminals beams out with a pod containing the resin, but then Picard reveals that he snatched a control device off of it. The criminal's ship promptly explodes.
- The Twilight Zone (1985): In "The Curious Case of Edgar Witherspoon", the titular character has been building an enormous, intricate Rube Goldberg Device out of junk, claiming to have been guided by a mysterious voice and that the device is needed to prevent The End of the World as We Know It. Dr. Sinclair believes he's crazy until he accidentally removes a few paperclips from the device, and a South Pacific island is swiftly destroyed by a tsunami, just as Edgar had warned would happen.
Radio
- A Running Gag in The Navy Lark is that any time a Floggle-Toggle is removed from a piece of machinery, it will either go wrong or stop working entirely.
Video Games
- Defied by the Car Mechanic Simulator series. The games will not let the player mount a part to something if a part is missing underneath. Only when the missing part is installed can the player mount the part that covers it.
- Several puzzles across Half-Life 2 require finding a missing piece of machinery in order to make a device work. For example, the elevator connecting the antechamber to the larval essence in Episode 2's "This Vortal Coil". When Gordon arrives to the zone after evading the Acid Antlion Guard, he's in a room with plenty of Barnacles and some Headcrabs, as well as broken catwalks and oxidated machinery. The zone of the elevator has a missing gear somewhere, and Gordon must retrieve it and place it where it belongs in order to make the elevator controls work.
- Kirby and the Forgotten Land: Fecto Elfilis is a biological example of the trope. After an undisclosed "warp experiment incident" occurred at the lab that was experimenting on them, a tiny piece of their psyche got separated from them and became a different character, Elfilin. However, when Elfilin went missing, Fecto Elfilis became too unstable to remain intact and turned into Fecto Forgo, who can't so much as leave the Eternal Capsule without melting into a puddle of blue-green gunk.
- Where in Time is Carmen Sandiego? (1997): In the Leonardo da Vinci level, the Monster of the Week built Leonardo a mechanical jester to entertain Mona Lisa to get her to smile. However, when the villain executed their assigned theft, they accidentally knocked several parts loose from the jester machine, and it quit working, leaving Leonardo at a loss to finish the portrait.
Western Animation
- Adventures from the Book of Virtues: In season 2, episode 3, Annie gets more orders for her craft weather vanes than she can deliver right away, so she rushes through them and skimps on parts to sell them on time — then gets complaints about how they're falling apart after being installed. This segues into a retelling of "The Horseshoe Nails" to deliver part of the aesop for the episode.
- Aqua Teen Hunger Force: After having the titular Chick Magnet delivered and set up in the episode "Chick Magnet", it appears to do nothing except occasionally roar. Master Shake concludes that a setting is off or a part must be missing but after Meatwad only finds a single screw left in the packaging, Shake dismisses it as irrelevant. At the end of the episode, Meatwad gets the screw inserted, and shortly after, every woman in town gets magnetically pulled to the Chick Magnet.
Master Shake: Throw it away! It's extra!
Meatwad: No, I'm sure the screw goes in here somewhere.
Master Shake: No! No! It's a double entendre... For the screwing that's gonna happen. - Arthur: In "The Boy Who Cried Comet", Buster and his friends build a telescope, but lose one screw. It turns out that this missing screw led to the telescope getting the comet's position wrong, causing the kids to wrongly think it will hit Earth.
- A case where sabotage ends up resulting in disaster for the saboteur occurs in Crossing Swords; Patrick the squire has a crisis of conscience over performing an execution. He decides the best course of action is to sabotage King Merryman's death machine, removing an otherwise innocuous bolt. When the criminal, who turns out to be Robin Hood in disguise, accidentally activates the death machine, one of the builders exclaims that the mercy bolt was removed. As it turns out, the mercy bolt was a key component to ensure a painless death. Patrick removing the bolt meant that Robin Hood's final moments were excruciatingly painful courtesy of King Merryman's death machine.
- Doc McStuffins: In "Starry, Starry Night", Aurora the sentient telescope has blurred vision, and nobody knows why. Eventually, Doc discovers it was because her eyepiece was left out when she was being built.
- Futurama: In "Less Than Hero", Professor Farnsworth orders a supercollider from an IKEA Expy. He has Fry, Leela, and Bender assemble the supercollider, and Bender remarks "Finished, and only 6 missing pieces". Whatever the missing parts were, they were obviously critical, as the supercollider explodes shortly after it's turned on.
- Handy Manny: In one episode, a man tries to build his girlfriend a robot that says, "I love you" in many different languages. However, the kit lacked an essential piece, which made the robot behave erratically, talk incoherently, and eventually fall to pieces.
- The Impossibles: In one episode, Multi-Man incapacitates the Puzzler by removing one of his metal pieces, stating that a jigsaw puzzle is useless if one piece is missing.
- The Looney Tunes Show: Daffy Duck learns that Bugs Bunny can afford his lifestyle because he receives royalties on his carrot peeling invention. Daffy decides that he can build one as well, and does so, cribbing from Bugs's earlier designs. Problem is, those early designs have a safety flaw that causes the device to overheat and catch fire. Daffy skipped the safety upgrades as "too much bother," and markets his hazardous peeler. It's not long before complaints from singed customers start to overwhelm Daffy, making him wish he'd never made the dratted device. Bugs Bunny grants this wish, which restores the old status quo.
- My Little Pony: Friendship Is Magic: In "For Whom The Sweetie Belle Toils," Sweetie Belle is mad because she worked hard to put on a play, but nopony remembered anything about it except her big sister Rarity's beautiful costumes. She feels like Rarity is always trying to upstage her, so she goes to her work room, finds an elaborate headdress Rarity is preparing for the pop singer Sapphire Shores, and secretly loosens a thread in it that is holding the entire thing together. Princess Luna shows her in a dream that if the headdress isn't fixed, it will fall apart at the moment of unveiling. Rarity will become a laughingstock and her fashion career will go down in flames, causing her to lose her mind, hole up in Carousel Boutique, and cut herself off from society.
- Exploited in the first episode of The New Adventures of Speed Racer. Rivals steal Mach 5 and copy it while it's lacking a single part. As soon as the heroes realize it, they tell Speed to use the hyperturbo mode. Once the rival driver does the same, his car, lacking that part, start falling apart literally within five seconds.
- Phineas and Ferb: "Phineas and Ferb Get Busted!" opens with the titular duo working on a landing tower for a Flying Car, Phineas being unable to find bolt #473. Once Candace successfully shows both parents the tower and car (due to them not disappearing due to outside interference like their other inventions), Lawrence decides that while the boys do need to be punished for building the tower and car without permission, said punishment shouldn't be too harsh since no real harm has been done. Right after Phineas finds bolt #473 in the grass and says he hopes it wasn't important, the tower promptly topples over and crushes a large portion of the family's house, resulting in both parents forgoing Candace's more harmless punishment suggestions in favor of sending the boys to a reform school.
- Pinky and the Brain: In "My Feldmans, My Friends", the Brain constructs a radio tower with the intent of broadcasting a fireside chat full of pro-him propaganda in order to Take Over the World, but the tower kit lacked a red rubber nub that is to be placed over the tip of the tower to prevent damages from the tip of the tower being struck by lightning (and because of the modifications the Brain made in order to hijack every radio in the world, a lightning strike would end up cooking the whole planet). After disassembling and reassembling the tower, the Brain orders a new rubber nub, which is delivered to his packrat neighbor Mr. Sultana "Barry" Sultana.
- Robot Chicken: One sketch features a LEGO space shuttle failing to launch, and instead crashing and bursting into flames. Following the deaths of the pilots inside, the NASA officer reveals the cause of the shuttle's crash: a 1x2 brick was missing from the assembly kit, and it was believed at the time that the workers could finish the vessel without affecting the demanding launch.
- Teenage Mutant Ninja Turtles (1987): The episode "Bye, Bye, Fly" has Baxter Stockman discover an ancient alien craft that has a transdimensional warp drive. He disassembles the warp drive into separate parts in order to lure the Shredder into a trap. However, unknown to Baxter, one of the disassembled parts ends up in the hands of the Ninja Turtles, which turns out to be a retaining bolt. Thus, when Baxter reassembles the warp drive without realizing he is missing a piece, his attempt to travel to Dimension X goes wrong as the alien craft ends up falling apart mid-transit.
- Thomas & Friends:
- The special Hero of the Rails focuses on Thomas finding an old rusty engine named Hiro and working together with the rest of the Steam Team to fix him in secret to make him presentable to Sir Topham Hatt (due to the possibility he would be forced to scrap Hiro in his current, worn-out state). They make good progress on repairing Hiro and only need Percy to bring one more part... when Spencer can be heard nearby, and Thomas and Hiro decide they need to rush the plan and get Hiro steamed up right now before Spencer finds them. Hiro is unable to run properly without the last part and falls to pieces while trying to evade Spencer, ending up in worse shape than when Thomas first found him.
- The special Thomas & Friends: The Great Race has Gordon fitted with streamlining for the Great Railway Show, and chooses to leave at the same time as everyone else rather than wait for his final safety check. Said safety check would have caught that the workmen forgot to install Gordon's safety valve onto his new streamlined body, causing him to overheat and almost explode at the Great Railway Show during the event's race.
Real Life
- A potentially catastrophic failure at a nuclear power plant in Britain was caused by a maintenance worker cutting corners, and routing three vital cables (part of the fault sensor system) through the same hole in the wall, with the result that all three were cut at the same time and the monitoring system went dead, thus blinding operators to the fact a potentially dangerous situation was happening. The worker involved, a relatively lowly carpenter who had no training in failsafe protocols, had reasoned that there was no need to route three cables through three different apertures spaced widely apart, as the plans demanded, and had opted to save time by drilling one larger hole and running all three through this. A mishap on the other side of the wall then cut all three cables simultaneously. note
- During World War One, Admiral Beatty of the Royal Navy decided it was a great idea to remove the flash protection from the magazines of his battlecruiser force to make reloading in combat faster. This, combined with limited armor protection against other capital ships and unstable propellant, resulted in two of his battlecruisers sinking from magazine explosions during the Battle of Jutland.note
- One historical myth holds that during World War II, an employee of the Eiffel Tower removed a single gear from the elevators (ensuring the Nazis would have to climb all the way to the top, preventing Hitler from giving a triumphant speech from there), and at the war's end, returned with the gear to restore the elevators. While Hitler was indeed prevented from making the speech, the cables were simply cut.
- The Jesus nut is a component that attaches the main rotor to the mast of a helicopter. Supposedly, it is named that because if it fails while the helicopter is in flight, the only thing left to do is "pray to Jesus."
