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"A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools."
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They are the bane of the Clock King. They are the worst nightmare of Manipulative Bastards everywhere. They are the monster in the closet that haunts The Chessmaster every time they close their eyes. Their very presence causes even David Xanatos himself to rethink all of his life choices in the blink of an eye.

Meet the Spanner in the Works.

Whether it's The Ditz, The Fool, Inspector Oblivious, or a monkey Geddit? , the Spanner in the Works is the miscreant capable of derailing the most ironclad of plans by unknowingly taking an option that the planner hadn't even considered. They ruin the implausible Gambit Roulettes by exploiting their one, intrinsic flaw: their reliance on Contrived Coincidences, rigid patterns, and the assumption that nobody would be stupid enough to actually push the Big Red Button or fight the apparently unstoppable robot.

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How can they outdo the master at his own game with nothing but stupidity and clumsiness? It's precisely because these characters are the fools and tools of fate that they are uniquely placed to derail these schemes with the gentleness of a butterfly flapping its wings... of doom!

Put another way, the Spanner is an author's walking deconstruction or Lampshade Hanging of the Theory of Narrative Causality: as easily as a plan or plot can come together, it can be pulled apart even easier with the tiniest, most ridiculous thing.

When the character ruins a protagonist's plans by unknowingly doing something small but crucial, he becomes an Unwitting Instigator of Doom. When the Spanner can trigger a series of coincidences, it's Disaster Dominoes. When the plan is screwed and the character is also aware that he will screw the plan, and doesn't care, he becomes a Leeroy Jenkins. Occasionally, may be Mistaken for Badass. If the focus isn't on them, they're often an Unknown Character.

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Compare Finagle's Law, It Began with a Twist of Fate, Nice Job Fixing It, Villain!, Outside-Context Problem, Remembered Too Late.

Opposite of the Unwitting Pawn, often is the Unwitting Pawn until the final crucial moment. This is the main cause of Didn't See That Coming, this trope being the "that". Quite often an Achievement In Ignorance. Inverse of Unintentional Backup Plan, where a character accidentally completes an imperfect plan that would have otherwise failed. Compare with Out-Gambitted, where someone's plan is (or could have been) successful but ineffective against a better-thought-out plan. Compare Too Dumb to Fool, where the character is too stupid even to be baffled by explanations. Also, compare Evil Cannot Comprehend Good, where the flaw is that the villain can't see someone being generous or brave or honest enough to foul up his plan.

The specialty of The Fool. See also Immune to Fate, for characters that manage to be this to Fate itself.

The trope is reputedly named for the Industrial Revolution-era practice of disgruntled workers throwing a spanner into a machine, either because of fears that machines would put them out of work, or as a bargaining chip for better working conditions (and often because they were the only ones who knew how to repair the machines as well).

(Note for Americans reading this: "Spanner" is the Queen's English word for what you would call a "wrench", with the added benefit of it being slang for a stupid person. It has nothing to do with a Long Runner in development. The equivalent American phrase specifically involves a monkey wrench, known in the UK as a gas grip — "He really threw a monkey wrench into my plans.")

Not to be confused with A Spaniard in the Works, which was a 1965 book by John Lennon of nonsensical sketches and drawings whose title was a wordplay on this expression.

Disgruntled French workers did this by throwing sabots (wooden-soled clogs) into machinery — giving us the word sabotage.

Often an ending trope, spoilers may be ahead.


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    Comic Strips 
  • Subverted in the Dan Dare series Reign of the Robots, wherein the only person that the Mekon paralyses after capturing the group is Dare's bumbling aide Digby, on the grounds that "he has no brain, therefore there is no predicting his actions".
  • In one week-long FoxTrot series, Jason finds it impossible to beat one guardian monster in a video game, as it instantly squashes his character every time he tries. Paige, who almost never plays video games, takes the controller and gets by the guardian by simply walking around him.

    Fairy Tales 
  • "The Three Snake Leaves": The princess' husband-murdering ploy could have worked if it were not for the prince's loyal servant witnessing the murder. Swiftly, he got into a boat, hauled the prince out of the water, used the snake-leaves to bring him back to life, and took him back to the king before the princess had the chance to feed her father one lie.

    Fan Works 
  • Abraxas (Hrodvitnon): Godzilla is a secondary character rather than the protagonist of this story, but he's responsible for kicking off the entire plot when he ripped San's head off of Ghidorah during the events of Godzilla: King of the Monsters (2019), leaving San and the Only Mostly Dead Vivienne inside his head separated from Ghidorah's malevolent influence before being reborn as the two-headed Monster X.
  • Adventures Of A Super Family: Lex Luthor's plan to destroy an upcoming company rival by sabotaging its experimental plane engine during an exhibit gets foiled when an unknown super-hero suddenly shows up and saves the plane.
    The plan had been so straightforward as to almost be laughable. Sabotage the plane's engine, making it crash, then blaming it on the new navigation system. Sure, any engineer worth his salt would say that a faulty navigation system would not make an engine explode, but with the plane splattered across half of Metropolis and a few hundred people dead in the crash, no one would have listened. The company would have never recovered from this public relations disaster.
    But the plan had not worked. All because some comic book superheroine had chosen that exact moment to step into the limelight. Was this a joke? Was some cosmic deity playing a prank? The world gains a superhero just in time to sabotage his plans?
  • Advice and Trust: Shinji and Asuka end up ruining Gendo's plans by befriending Rei, although this happens long before his plans are put into action. And everyone is completely unaware of the implication of this, meaning that they spend several chapters trying to figure out how to stop him, and he still thinks that he's in control of the situation, despite the fact that he's already lost.
  • An Alternate Keitaro Urashima repeatedly derails his grandmother's attempts to manipulate him simply by letting others know how manipulative she is. As a result, when she shows up and starts spinning her webs, she winds up proving him right.
    • Mokoto also runs afoul of this when she threatens Keitaro one time too many. When she draws her katana, she's unaware that some police officers are passing behind her and witness it.
  • And the Giant Awoke: When Euron and Tywin make their plans for dealing with each other - raid into the other's lands to force the enemy to retreat and fight in their own terms - all of them are for nothing when a storm forces both fleets to change course and they meet in the middle of the sea.
  • Ranma becomes one for not only Minaka and his Sekirei game in Anything Goes Game Changer but Higa as well, the latter without even being aware of the man's existence. Besides Ranma interfering with unfair battles, mostly preventing Sekirei from being forcibly winged, he and Uzume pose for pictures for Nabiki to raise money (to cover his living expenses). Uzume's cut is enough for her to pay off her Ashikabi's hospital bills, which were being used by Higa to blackmail her.
  • Atonement: The Slaughterhouse Nine might have gotten a new member in Ruin had Mnemosyne not interfered, turned Burnscar against the rest of the Nine, and freed Hunter.
  • Avatar: The Last Alicorn: Sweetie's plan to take over Fillydelphia and eliminate all the water and fire benders along with the avatar and the great dragon would've gone perfectly, if it wasn't for AJ learning metal-bending, allowing her to escape, and provide Team Avatar an avenue to escape.
  • The Bridge gives a borderline humorous example in an otherwise completely serious situation. Bagan has set up an elaborate Xanatos Gambit that would work out in full to both secure more power for himself as well as kill Harmony. A crux of it was keeping a displaced Monster X separated from his comrades and put into the Equestria Girls world, where he'll be weaker in his human form and thus easier to kill by Bagan's agent, Enjin. One bystander messed it up and they weren't another kaiju nor an Equestrian hero intervening in the fight. EG!Photo Finish happened to be at the scene of a battle between X and Enjin at a hospital and took some pictures, thinking it was a movie stunt being filmed. Days later when an ally of X was in the same realm but dozens of miles away, she bumped into Photo, saw the pictures and recognized X in the images; and was able to alert her allies that she'd found him and he was in trouble. Bagan, the billions year old Physical God got his plans set back by a photographer who didn't even know what she was snapping pictures of.
  • In Cardcaptor Rad, the Decepticons plan to invade the Autobot base actually works. They likely would have succeeded in attaining the Star Saber if not for the humans and mini-cons being there.
  • Fate/stay night's fanfic Chaos Theory opens up with this. It introduces the plots and manipulations of all the antagonists of FSN, and then the narrator calmly declares:
    "But mostly? The assorted plans at play here would be going very, very wrong due to the actions of a no-name, no-count, utterly talentless Magus by the name of Shirou Emiya. He had no magic worth mentioning, no combat experience of note, and no plan for or knowledge of the War he was about to enter. He did, however, have one trait that had derailed a countless number of such grand, far-reaching schemes throughout history.
    You see, he really, really wanted to be a hero."
  • The Child of Love:
    • Gendo thought he had planned for any contingence but he did not foresee his son's involvement. Shinji sleeping with Asuka forced him to modify his plans and it ensured that Yui would want to protect his son’s family and Rei would get involved in ways Gendo would not like.
      Fuyutsuki: But you said that this project was 100% planned, right?
      Gendo: There was only one mistake on my part. I won't let that happen again.
      Fuyutsuki: You mean...your son?
      Gendo: Yes. I didn't think that the Second Child would use the Third to 'satisfy' her boosted hormones...this was a big mistake, and may result in complications.
    • In chapter 9 Fuyutsuki warned him that he had not accounted for everyone and someone would stop him, but Gendo did not listen. Cue Rei interfering. And then Yui.
      Fuyutsuki: I think you're forgetting about someone. Someone who won't forgive you for this, Rokubungi Gendo..."''
  • Children of Remnant: Fifteen years of indoctrination by Salem begins to be undone by Yang deciding to throw the Claimed a party.
  • The Choices Of Earth: Agent Johnson and the Torchwood team’s other government contacts are completely caught off-guard by the Doctor’s involvement in the situation.
  • The Chronicles of Tanya the Holy: Tanya ends up being a massive spanner for not just the Lich King, but for the whole plot of Warcraft III. First is her actions in Stratholme where she calls upon Being X and purifies all the infected villagers on top of crippling Mal'Ganis. Then in Northrend, Tanya stops Arthas from taking up Frostmourne and psychically damages the Lich King. Besides Arthas never joining the Scourge, the Alliance is reformed, Quel'thalas is never sieged, the Burning Legion doesn't return, and the Horde and Night Elves become trading partners, though the last part doesn't last.. In the epilogue, it's revealed that Tanya threw things off so much that the Bronze Dragonflight went insane and had to be put down after they started attacking the Alliance in an attempt to set things back on the "correct path".
  • In the Mario Fanfic Clash of the Elements, Fawful, Alpha and Mario are this to Cackletta's plans. And Bowser too, for freeing the Star Spirits from their imprisonment.
  • Code Geass: Paladins of Voltron: C.C. following the Paladins to the Castle of Lions is this for Charles and Marianne, as this puts her beyond the range where the latter can track her.
  • Examples in My Hero Academia fanfic Conversations with a Cryptid:
    • Midoriya discussed this with All For One, as he discovers that something must have happened for the murderous supervillain to put his plans on hold. All For One cryptically says that plans can change. In fact, it was because of his marriage to Inko and Midoriya being born that caused All For One to change his plans so he could stay with them and/or keep them safe.
    • Another spanner is the Sludge Villain who proceeds to kidnap Midoriya, eventually resulting in All For One breaking out of prison to rescue his son.
  • Death Note Equestria: Mer ends up going off Twilight's script in order to ruin her in revenge for Rarity's death as a part of one of Twilight's earlier gambits. Subverted, however, as Twilight had actually anticipated this and factored it into her plans, resulting in Twilight's triumph and Mer's death.
  • Devil's Diary: Before his first outing, Magneto looked into the then-current cadre of heroes and villains and decided neither of them would want or be able to stop his coup. Yet still he was driven away by five heroes who nobody had previously seen before... although he KNEW who they were working for.
    Damnable adolescent yearlings, every one of them, like the beardless youths Hitler put against the Allies when all his other defenses were cracking. Except these yearlings had power. None of them equal to mine, individually. But they knew how to effectively combine what they had. And they had luck, three times damned three times luck, and NO ONE HAD EVER SEEN THEM BEFORE.
    All mutants.
    Three males, one female, and one snow-being whose sex is impossible to determine at this point.
    An unknown quantity.
    An x-factor.
    A XAVIER FACTOR.
  • In crossover fanfic Displaced: Spider-Man's arrival in Gotham City and his meddling with a Joker's heist accidentally causes an unprecedented gang war all across Gotham.
  • Doing It Right This Time: Asuka has grand ambitions to being this after realising she's in a Peggy Sue situation, but the one to take the biggest direct step towards derailing the Scenario is Rei... and to a lesser extent, the late Naoko Akagi. Shinji still needs some convincing that they can pull it off.
  • Echoing Silence: When Celestia banished Twilight, she thought that Twilight was on the verge of going Nightmare, and either would, or be returned to normal by guilt, either of which Celestia had plans to deal with. Unfortunately, the changeling invasion prevented Celestia from looking for Twilight when she wanted to.
  • Ironically, Black Wizard Zeref becomes one for one of Grimoire Heart's plans in Fall of the R-System. His arrival to destroy the R-System a cult was making distracted and kept Ultear from brainwashing Jellal with a false ghost of Zeref.
  • Fate/Harem Antics: The entire fic is about Irisviel, who is trapped in the Holy Grail but in full control of it, deciding to use the upcoming Holy Grail War to get her son Shirou a harem. All the existing plots and plans promptly get derailed as Iri makes sure all the Masters and Servants besides Shirou are female. Specific examples are:
    • Iri's father planned to summon Hercules as a Berserker and force his granddaughter Illya to serve as Master. Iri summoned Minamoto no Raikou instead. Likewise, Iri has some limited ability to speak to her daughter through the Grail, so unlike in canon where Illya hated Shirou and their father (because her grandfather lied to her), Illya knows that their father never abandoned her, and is looking forward to meeting Shirou.
    • Bazett tried to summon Cú Chulainn as Lancer, but Iri gave her Scáthach instead. More importantly, when Kirei tried to murder Bazett for her Command Seals, Iri briefly stopped his artificial heart, distracting him at a critical moment and ruining the opportunity.
    • Sakura summoned Medusa as Rider, as in canon. Zouken tried to force Sakura to give control over to her brother Shinji, but Iri deliberately made the summoning more explosive than usual, causing the ceiling to fall on Zouken. Sakura and Rider escaped in the confusion.
    • After Zouken recovered from having a ceiling drop on him, he summoned a Servant himself, deciding an Assassin would fit him best. Iri gave him Hassan of Serenity, a Poisonous Person. Zouken didn't realize that, slapped her for her perceived disobedience, and melted. And since Iri had severed his connection to Sakura (which she could only do after Sakura made her contract with the Grail), he couldn't draw power from her and stayed dead for good.
    • Iri did this to herself with Assassin: Since the intent is for Shirou to have sex with all the girls, the fact that she can't touch anyone without killing them is a problem. Iri quickly summons Sir Galahad as Shielder, who has the power to resist poisons and can pass this onto her allies. And she makes Caren, Kirei's long-lost illegitimate daughter, her Master just to mess with Kirei.
    • And Iri again manages to do this to herself. By summoning Shielder and Ruler, she broke the normal limits on number of Servants and left the door open for others to be summoned. Three separate groups start summoning Servants of their own. Iri can't shut them down, but she can make sure the Servants and Masters are all female. She gives the Ainsworth family Jeanne Alter as Avenger, but instead of letting Julian become the Master as they intended she grabs his sister Angelica. She gives Fiore of the Yggdmillennia clan Oda Nobunaga (who is female in the Nasuverse) as Gunner. And Miyu wasn't trying to summon a Servant at all, but didn't understand how the Grail War worked and got Elizabeth Bathory as Temptress.
  • Nanoha's presence in Game Theory derails Precia's carefully laid plans. But this turns out to be a subversion, because the events that disrupted Precia's original strategy actually made it possible for her to come up with a better plan that works flawlessly.
  • Guardians, Wizards, and Kung-Fu Fighters:
    • During the Battle of Torus Filney, the Rebellion's strategy hits a major stumbling block when Simon shows up, due to not having planned for his presence. But then they're able to turn the tables on Servantis' forces when they reveal that they have guns.
    • Cedric and Wong's plot to betray Phobos and steal the Heart of Meridian from him catches Nerissa completely off guard, throwing her own plans completely Off the Rails.
  • In Harry Potter and the Alien Reality, Harry represents an unexpected factor to most villains faced by the SGC as none of them are used to facing magic, although SG-1 take care to ensure that Harry doesn’t do anything to expose his magic to the Goa’uld even if the NID are aware of his magic.
  • Hellsister Trilogy: During the Apokoliptian War, Darkseid is always at least three steps ahead of his enemies, and he comes very close to win. His plan only fails because of one factor he couldn't have foreseen: Supergirl being near from D'reema right when he spoke the Anti-Life Equation. Before succumbing to the Anti-Life Equation, which destroys Free Will, Kara had just enough time to hypnotize D'Reema into speaking the opposite Equation, thus cancelling out its effects.
  • HERZ: SEELE’s attack in 2015 failed because another secret organization accidentally learnt about their plans and interfered with them… something SEELE had not counted on at all.
  • Higher Learning: Gendo’s plan started to unravel when a teacher offered counseling to the Children.
  • A History of Magic: The Incubators feared that this would happen in the form of an Anomaly, a person who has magical powers not granted by them, for they could awaken the magical powers in all of humanity. It was why they had arranged for Jesus to be crucified, after all. Their fear was eventually realized when Billy Kane used Haitian magic to become a Puer Magi, causing a chain reaction that resulted in thousands of teenagers spontaneously becoming Puer and Puella Magi without contracting.
  • Jewel of Darkness: The only reason Midnight's plan to torture Robin to insanity fails is because Ai betrays her on orders from Trigon, something she couldn't have possibly anticipated.
  • In Kage, Yua predicts Jade's presence in Meridian will cause Nerissa's plans to go Off the Rails, and any attempts by the elderly sorceress to force Jade to fit in her plans will only cause the schemes to unravel further. Jade is also this to the second season timeline in general, with the changes already starting to add up.
  • The Karma Of Lies: Both Gabriel and Nathalie plan to use the secret Agreste emergency fund account for their own schemes. Unfortunately for them, Adrien also knows about said account; it's the only one he's able to access. After he foolishly accesses it right in front of Lila, she memorizes the passwords and secretly cleans him out, leaving just enough money for the checks he wrote to go through.
  • Kara of Rokyn: Lex Luthor's plan to kidnap his sister Lena and his nephew fails because his enforcers accidentally stumble on Captain Strong, who looks like a regular old guy but is in fact a vicious, super-strong street brawler. Knowing nothing about him, they underestimate him and are brutally beaten up.
    Luthor's enforcers had learned to respect superheroes and never take a foe for granted. Chances are, the old guy facing them was tough, a brawler, but they could handle that. They were also three or four to one, depending on how you counted the Siamese twins, Pluto and Plato Statler.
    The problem was, nobody had ever briefed them on Captain Strong.
  • Know Thyself: While Voldemort was a carefully crafted factor in the machine's plans, Harry surviving his encounter with a scar and Voldemort's code being scattered from it was such an anomalous event, agents had been keeping a close an eye on him to ensure that he wasn't a threat up until the point that Trinity found him. Not only that, but the machines didn't even notice his absence at first because he is the only wizard to have been successfully unplugged, all other attempts rendered in a vegetative state.
  • The Fairy Tail AU fic Lost Magic is an interesting example. While the deliberate wrench in Jellal's plans is Simon, the one whose mistake actually set his plot derailing was Jellal, himself. By accidentally getting himself pregnant with Erza's child.
  • Ned Stark Lives reveals that Jaqen H'ghar had been hired by the Great Other to kill Jon. Arya's presence in the Night's Watch caravan completely derailed that plan, though.
  • New Beginnings (Smallville): After being exposed, Clark intends to go back a few days in order to discredit Linda Lake's before she can out him. Linda's interference, though, causes him and Lois to travel all the way back to 2001.
  • Queen of All Oni: Jade's otherwise flawless Operation: Steel Lightning only fails because of the presence of Agent Wisker, who she didn't know and couldn't plan for. He doesn't stop her, but slows her down long enough for Uncle to catch up with her and beat her.
  • Quicken: Emma accidentally and inadvertently causes a gang war only because she was in the wrong place in the wrong time wearing the wrong clothes.
  • The Pony POV Series has one that's notable for the exceptionally long time required for the spanner to actually get into the villain's works. Back in the G3 Universe, which was facing The End of the World as We Know It (actually a Shoot the Dog to avert a Class Z Apocalypse) at the time, Pinkie Pie's best friend Minty just bled to death after their fight with Luna, leaving behind her "spirit" (or at least a piece of herself). Strife, Discord's sister and Spirit of Natural Selection, is fighting the survivors of the doomed world (in order to give them at least the chance to fight for their survival, something she believes is the right of all living things) and sent Heartless-like spirits of "erased" ponies after them. One of these falls into the canyon where Pinkie and Minty's fight took place, wounded in battle. Pinkie, in a split second choice, fuses the piece of Minty with the shadow, which turns out to be that of the G1 Twilight. The result? Twilight Sparkle!
    • During the Dark World Arc, Discord's little sister Rancor is this. She arrives to get close to Discord and ultimately steal back Destruction's power from him so it can be used for its intended purpose (Destruction's original job as an Anthropomorphic Personification), mortally wounding him in the process. This ends up throwing a gigantic wrench in Nightmare Eclipse/Paradox's plans, allowing Discord to Out Gambit her and alert Twilight to the true nature of the Dark World, forcing Paradox to expose herself to the heroes. The name Rancor chooses after succeeding (Disruption) couldn't be more appropriate. It's this trope especially because, while its implied she knew Paradox was there, she didn't care one way or the other what happened so long as her own mission was a success.
    • Part 6 of Shining Armor's Arc has Sergeant Thunderchild be this General-Admiral Makarov's attempt to kill Shining Armor. Makarov didn't even know his name, yet he shows up just in time to break through Makarov's Anti-Magic field and save Shining. This also buys time for more Shining's forces to show up in a Gunship Rescue and drive Makarov's forces off.
    • During the Wedding Arc, Prince Blueblood inadvertently foils Queen Chrysalis' plan just because he wanted to take a girl on a date. He led his date through the caves under Canterlot, and ended up finding the imprisoned Princess Cadance.
  • In Evangelion fan-fic RE-TAKE, SEELE finds all their plans foiled by something they could never have anticipated Shinji be aided by Ghost-Asuka and "God" which allows him to destroy the Mass Production Evas during the fan-fic's take the events of "End".
  • In The Matrix fic Rescue Run, Captain Dena Reese unknowingly serves as this to the Machines' cycle of control to keep the human population of Earth under their control; not only does she confirm that the Matrix has existed for longer than the two centuries the people of Zion believed, but she also helps them make contact with the human colonies in the rest of the solar system. Through her presence, the people of Zion are evacuated from Earth and relocated to a new green planet, while the spacefleet destroys the Machine mainframe and the Matrix to prevent the machines following them into space.
  • The escape sequence in Revan's Story is a series of spanners caught in other spanners. Like in canon, the protagonists anticipate capture by the ship Leviathan, so they each come up with a plan to escape and free the others. Unlike in canon, Darth Bandon throws a wrench in their plans. First, he stops HK and T-3's plans because he recognizes Revan's personal assassination droid, and orders his troops to wipe their memories and physically restrain them in case the wipe doesn't go deep enough. Second, he stops Jolee's plan to Jedi Mind Trick the guard into solitary confinement because he knows what the trick looks like. Third, he senses Juhani sneaking through the Force and overpowers her. Canderous's plan of faking his death is eliminated for being risky, and Zaalbar is absent. Only Mission's plan goes undetected by virtue of not starting until she's away from Bandon, and even then she's almost caught. The party isn't recaptured because Admiral Karath, the last spanner, was also The Mole.
  • Spider-X: Mystique’s immediate plan to spend time with Rogue as Risty and her and Magneto's more long-term plan to infiltrate the manor and pose as Xavier are both thwarted just because Peter Parker joins the X-Men, as his spider-sense makes him aware of Mystique's true identity even when she isn’t explicitly doing anything dangerous (although she doesn't actually know how he sensed her for some time).
  • Team 8: In Chapter 17, Kurenai tells Naruto to use his chakra pulse to dispel the genjutsu Kabuto put on the stadium. Naruto overpowers the pulse so much it ends up covering the entire village - causing Orochimaru's plan to fall to pieces twice over, as not only did it dispel the jutsu that were going to summon the giant snakes, it also destroys the barrier he had put to prevent people from interfering with his duel with the Third Hokage.
  • In this Ten Little Roosters fancomic series, every one of Barbara's attempts (and traps) to murder their Rooster Teeth colleagues is foiled due to the others' sheer dumb luck (with a few cases of taking a level in intelligence). The result? Everyone ends up surviving:
    • Michael's poisoned glass breaks before they have a chance to drink from it.
    • Gavin and his clone manage to catch themselves, preventing them from falling in the mousetraps.
    • None of the arrows wind up hitting Chris.
    • When reaching for the extra gun, Burnie spots the scorpion and shoots it.
    • [[spoiler Gus]] slams the door on the Killer.
    • Adam trips over a cord just as the Killer is about to strangle them.
    • The puma decides they're more interested in being petted by Lindsay than mauling her to death.
    • The part of the treadmill that Miles is glued to breaks off completely.
  • This Bites!:
    • The Unluckies. If the For Want of a Nail in Chapter 19 wasn't enough, in Chapter 20, Cross attempts to use Soundbite's powers to stop or stall the Rebel Army outside of Alubarna. Unfortunately, the Unluckies arrive and snatch the snail, scrapping that plan. And even after they're beaten, Miss Friday manages to disable Soundbite's powers until Luffy beats Crocodile.
      • For a while, it actually became something of a Running Gag that the Straw Hats' plans never worked out as planned, to the point that the characters started making note of in their planning sessions. This was particularly frustrating and humiliating for Cross, as he is the official tactician for the crew. But starting after Skypiea, things start going much better.
    • Granny Kokoro proves to be this to Cross's plans. Sloshed out of her mind, she browbeats Iceburg and Franky into feeling the love that the Going Merry has for her crew, and encouraging them, as Tom's apprentices, construct a ship worthy of the Oro Jackson's successor... within earshot of Iceburg's secretary and one of his best shipwrights.
    • Aokiji. Post-Enies Lobby, when he came across an island hosting a big pirate brawl, he decided to halt the whole thing with an Ice Age... giving Blackbeard the perfect opportunity to swallow up his now-frozen opponents.
  • In Ultimate Sleepwalker: The New Dreams, the Green Goblin kidnapped and planned to publicly murder Gwen Stacy as a way to get revenge on her father, Captain George Stacy of the NYPD. While Spider-Man intervened and tried to rescue Gwen, the Goblin had anticipated that and set things up so he'd be able to kill both Spider-Man and Gwen at the same time. Unfortunately, what he didn't take into account was Sleepwalker following Spider-Man to the top of the bridge a Cascnd distracting him long enough for Spider-Man to rescue Gwen and get her to safety. The Goblin proceeded to have a Villainous Breakdown.
  • In The Vow (an Alternate Universe Fic of Kung Fu Panda 2), when Po and the Furious Five have been imprisoned in the dungeon of the Tower of the Sacred Flame and Shen prepares to spring his trap for the invited nobility of China, Lianne sends Jade to free the heroes before they can be killed, allowing them to rescue the nobility, setting back Shen's plans of conquest a little.
  • Harmony acts as one in We're Doomed to Marcie Ross and her plans to murder the popular kids as revenge. Namely, when Cordelia is running from the invisible monster trying to kill her, she runs right in front of Harmony's car who swerves to avoid her, right into Marcie. Harmony also ruins the plans of the organization seeking to recruit Marcie.
  • Xander in Xendra functions as a spanner on a cosmic scale. Not only can Drusilla the Mad Seer not See him and thus can't counter his plans, but he's shown to be immune to prophecy, leading to him breaking three or four prophecies, including Jasmine's plan to be reborn via Cordelia.
  • Zuma's Fear: Believe it or not, Zuma ends up screwing Stone’s Evil Plan after the death of his family.

    Films — Animation 
  • Aladdin: Jafar's plan to steal the lamp and leave Aladdin behind in the cave would have worked if Aladdin's pet monkey Abu hadn't picked his pocket and then given the lamp to Aladdin. Though Jafar kind of did this to himself as well as Abu wouldn't have done so if Jafar hadn't attempted to kill Aladdin.
  • Beavis and Butt-Head Do America has two of them:
    • The first are the crooks who break in and steal the two's TV. This is what prompts them to search for it (or a suitable replacement) and making their way to Muddy Grimes, who drunkenly mistaken them for the two crooks and sends them to "do" (re: kill) his wife.
    • Beavis and Butt-Head are the other spanner. Dallas Grimes uses the boys' libido to get them to go to Washington, DC, hiding a deadly virus in Beavis' pants. Instead, their crazy road trip separates the two from Dallas, leading to her and Muddy getting arrested and the virus back in the hands of the US Government.
  • In Home, Pig the cat's presence spare Tip from being abducted with the rest of the humans. When the Boov are collecting the humans, Pig panics and clings to Tip's head. The scanner detects Pig instead of Tip and disregards them both, causing Lucy to be taken alone. Were it not for this twist of fate, Earth and the Boov would likely have been destroyed.
  • The Little Mermaid: Scuttle is the recurrent reason Ursula's con on Ariel fails and the film doesn't have the same Downer Ending as the original fairy tale. Not only does he catch Ursula gloating about her plan in her disguise and warn Ariel she has been duped, he arranges the other ocean creatures to stall her wedding with Eric, as well as smashing Ursula's conch to grant Ariel back her voice and break Eric from his hypnotic state so he could pull a Big Damn Heroes.
  • Monsters, Inc.: Mike forgetting to file his paperwork, and Sulley volunteering to get it for him, end up causing a chain of events that exposed Randall and Waternoose's plan. Roz gives them credit for exposing the scandal when she reveals her own true colors.
    Roz: Two and a half years of undercover work were almost wasted when you intercepted that child, Mr. Sullivan. Of course, without your help, I never would have known that this went all the way up to Waternoose.
  • My Little Pony: Equestria Girls
  • My Little Pony: The Movie (2017): When Tempest sends the orb to petrify Twilight, two different pegasi dash in with the aim of saving Twilight. Rainbow Dash saves her, while Derpy Hooves Takes The Bullet and the resulting distraction buys the Mane Six their chance to get away.
  • Lord Farquaad in Shrek. By sending the fairy tale creatures to Shrek's swamp, he is the reason Shrek sets out to find him in the first place. He sent Shrek to get Fiona so Farquaad could become king in exchange for his swamp leading to Shrek and Fiona meeting. Fiona falls in love with and marries Shrek, which foils the plans of every subsequent villain in the seriesnote .
  • Teen Titans Go! To the Movies: Slade-as-Jade made sure every superhero was distracted by them having their own movie, even The Challengers Of The Unknown. What he didn't count on were the Titans, who had no movie and therefore were the only ones who confronted Slade at S.T.A.R. Labs, and he really didn't count on them being competent enough to grab the MacGuffin away from him, countering his moves. This drives "Jade" to try to distract the Titans by Divide and Conquer while making the Robin movie the main vector for his Mind-Control Device.
  • Woody, Chatter Telephone and Chuckles turn out to be the keys to dissolving Lotso's reign over Sunnyside in Toy Story 3. With Chatter's help, Woody breaks out all of his friends and escapes with them out the trash chute (a feat rarely done without being broken), sends Lotso into a Villainous Breakdown by presenting him with Daisy's locket (which Chuckles saved) and ultimately gets him banished to the dump, freeing Sunnyside from his corruptive influence.
  • The title character of Wreck-It Ralph. His desire to gain the fame and respect his rival, Fix-It Felix, Jr., had, even unwittingly, lead to Sugar Rush's King Candy being exposed as the thought-dead Turbo and the restoration of glitch character Vanellope Von Schweetz.

    Films — Live-Action 
  • The Adjustment Bureau tries to contain this kind of incidents. But they are not above random chance and unexpected behavior.
  • In American Animals, the first attempt at the robbery gets abandoned because there are multiple librarians in the rare book room, and the gang has no contingency for dealing with this.
  • In Andhadhun, Mrs. D'Sa witnessing the comings and goings at the Sinhas' apartment and telling the police results in both Simi and Manohar's plan (simply framing an innocent man and then moving on) and Akash's plan (feigning ignorance to avoid putting himself in danger) being thrown off course. Simi's attempts to course-correct further complicate matters.
  • In The A-Team, Face's plan would have gone off smoothly if not for Pike having a SMAW.
    Pike: Here's what I think of your best laid plans!
    [Pike fires the SMAW into the ship's hull]
  • In The Atomic Brain, as shown on the TV series Mystery Science Theater 3000, in spades. The main plot for the villain Miss Marsh was for her to have her brain swapped with the prettiest girl of three chosen. That gets ruined when the homeliest of the three, who had her brain swapped with the cat's, gouges her eye out. Miss Marsh's companion tries to double-cross her, killing her and letting the remaining girl take her money, but Marsh kills him. The scientist, Dr. Otto Frank, pulls one by placing Miss Marsh's brain with the cat's, revealing that he wanted to keep her locked away in the cat so he could use her money to continue his research on reviving the dead. Miss March responds by locking him in the revival chamber and setting the dial to "Frag the entire house".
  • The Avengers:
    • Had Thor not been there to keep the Hulk at bay the Helicarrier would have crashed and Loki's plan would have more than likely been successful.
    • The arc reactor in Tony Stark's chest. It prevents Loki from mind-controlling him and turning him against his allies, which would have derailed everything just as much as the Hulk's potential rampage.
  • Beetlejuice would have succeeded in marrying Lydia and be able to stay in the world of the living forever, if it wasn't for the Maitlands. Adam manages to drive a miniature car into Betelgeuse's foot, which distracted Betelgeuse, while Barbara comes into the house, riding on a sand worm that ends up eating Betelgeuse stopping the wedding from happening.
  • In Big Game, the villains' meticulously though-out plan is derailed by Oskari. If he didn't find the escape pod with president in, the only thing to do would be to open the door and pull the trigger. As it is, they end up chasing the two of them throughout Finland and fail.
  • In The Butchers, JB's original plan was to resurrect the six Serial Killers and then kill them so he could absorb their power. What he didn't count on was a busload of tourists being stranded in the Ghost Town on the day he planned his ritual, or two of those tourists triggering the ritual early. The end of the film implies that Satan, in the guise of the bus driver, deliberately led the tourists there to thwart JB's scheme.
  • Carlito's Way ends in a similar fashion. After outsmarting all his enemies by the skin of his teeth Carlito ends up getting killed by some random lowlife he mistreated earlier in the film.
  • In Cast a Deadly Spell, the Evil Necromancer's plan to summon Cthulhu is thwarted when it turns out his daughter was no longer a virgin due to the idiot cute cop nobody had been paying much attention to.
  • Con Air features the Ax-Crazy Cyrus the Virus, who plans to take over the Fairchild C-123 plane Jailbird before it drops him off to a new Supermax prison and has several very dangerous criminals willing to help him. Too bad that one of the passengers just happens to be a guy on parole named Cameron Poe, an ex-Army Ranger who takes absolutely no shit from anyone and will do anything in his power to stop Cyrus and Co. so he can go home to his family.
  • The Dark Knight Trilogy:
    • In Batman Begins, Batman himself is the Spanner towards Ra's al Ghul and the Scarecrow's plan to destroy Gotham.
    • By refusing to sacrifice each other, the passengers on the two boats end up being this for The Joker in The Dark Knight, in that his social experiment in proving that anyone could be corrupted ends in failure.
    • And in The Dark Knight Rises, Catwoman serves as one when she saves Batman from Bane in the climax.
  • In Day of the Wolves, #1's plan for Taking Over the Town was masterfully planned and executed. The one thing he could not have foreseen was that Chief of Police Pete Anderson would have been fired the day before the plan was executed, and therefore was at home instead of at the police station with the other officers.
  • Deep Rising: The cruise ship's owner had intended to fake a pirate take-over by hiring mercenaries to rob the passengers, force them into the lifeboats, and then sinking the ship so he could collect the insurance money. He (nor anyone else for that matter) certainly didn't count on the cruise ship being attacked by a hungry Sea Monster before the mercenaries arrived.
  • The scheming husband in Dial M for Murder is undone because he underestimates the intelligence of Swann/Lesgate, the thug he hired to kill his wife. Swann puts the key right back after using it, rather than keeping it, as his employer expected.
  • Die Hard: Cowboy Cop John McClane's real job. When terrorists are confidently moving chess pieces behind the scenes, he knows that all he has to do is look for something sensitive and start whaling on it.
    • He even invokes this in all but name in the first film when Hans Gruber demands to know who he is.
      McClane: Just a fly in the ointment, Hans. The monkey in the wrench. The pain in the ass.
    • In A Good Day to Die Hard, Komarov has convinced long-time rival Chagarin that Komarov has a file on all of Chagarin's evil plans. Komarov intends for Chagarin to free him and then use his resources to steal uranium stockpiled at Chernobyl. The first spanner is that Komarov didn't expect the CIA (also believing the file to be real) to break him out of prison before Chagarin could. And the second spanner is, of course, McClane who's come to Moscow to help out his son John and ends up ruining everything.
  • Lara Lee in Django Unchained is the one who first notices Hildy's tension with Django, and it's her lighthearted jest about it that draws Stephen's attention to them enough for him to work out the rest. It's possible that the plan would have gone off without a hitch had she not noticed or not chosen to joke about it.
  • In the 1932 sci-fi mystery film Doctor X the Mad Scientist Serial Killer manages to not only trick the other characters into believing he is innocent but also manipulates them into physically restraining themselves so he can slaughter them at his leisure. Unfortunately he forgot about the Plucky Comic Relief Intrepid Reporter, who manages to dispatch him in a terrified and bumbling fashion at the last minute.
  • This concept drives the entire plot for Dumb and Dumber. Lloyd sees Mary "forget" her briefcase while going through the airport, and, desperate to win her affection, races through the airport to snag the briefcase and return it to her: the briefcase is the drop for a ransom, containing millions, left there to be picked up by a few hired thugs. The entire plot also runs because the crooks think that Harry and Lloyd are merely Obfuscating Stupidity, never understanding that no, they are actually that dumb, but happen to thwart the criminals at every turn.
  • In A Few Good Men, it becomes apparent that the Department of the Navy very much wants the case of United States v. Dawson & Downey to be quietly resolved by a Plea Bargain so as to prevent incident from causing too much embarrassment to the Marine Corps. This plan is undone by the dual spanners of Galloway and Dawson; Galloway, because she senses something isn't right, and goads Kaffee in doing his due diligence for once instead of rushing to a Plea Bargain. Dawson, meanwhile, is too hardcore of a jarhead to willingly accept a dishonorable discharge because it'd be easier for him, telling Kaffee to take his plea bargain and shove it.
  • Forrest Gump calls to complain that he can't sleep because of people playing with flashlights in the next building over, and so blows the lid on Watergate.
  • In Godzilla vs. Destoroyah, Godzilla spends days suffering a nuclear heart attack without even realizing it.
    • Godzilla vs. Kong: Team Godzilla. Unlike Team Kong, whose actions are essential in moving the plot forward, Team Godzilla's only role up until the Final Battle against Mechagodzilla is discovering the conspiracy behind Apex. While important for the audience's sake, it's technically inconsequential in the grand scheme of things — until they manage to sabotage Mechagodzilla's remote control panel at a pivotal moment, giving Kong and Godzilla enough breathing room to finish it off. If they hadn't been there, Mechagodzilla would've killed both Godzilla and Kong before going on to destroy what was left of Hong Kong and likely the rest of the world.
  • Goosebumps: Usually whenever one of the Goosebumps manuscripts is unlocked and a monster escapes, Stine manages to capture it and he and his daughter are forced to move. When Zach releases the Abominable Snowman, however, the bookcase collapses and Slappy escapes as well. Slappy then proceeds to release every monster R.L. Stine ever created and burns the manuscripts for good measure.
  • In How to Rob a Bank, Simon's carefully planned Bank Robbery goes to hell when Simon, The Everyman who only came in to complain about ATM fees, locks himself in the vault, accidentally taking the crew's computer expert hostage in the process.
  • In Jurassic Park, Nedry has a very well-thought out plan to steal the dino embryos and whisk them to a waiting boat. He's plotted a perfect 18-minute window to be back before anyone knows it with a minor computer glitch to hide the theft. But a hurricane suddenly changing course to hit the island was never in his plans. It leaves Nedry racing and driving in the rain to get lost and eventually to his death.
  • In The Caper film The Killing, a band of criminals pull off an elaborate robbery of a racetrack. Even though the most of the criminals kill each other off fighting amongst themselves, the Anti-Hero and his Love Interest manage to escape to the airport and prepare to board a plane out of the country with all the loot. However, all their plans are foiled when a dog runs out in front of the luggage train, causing it to crash and spill the loot all over the runway for all to see.
  • In Kingsman: The Secret Service, Valentine's plan would have gone off without a hitch if Harry hadn't pulled Eggsy to his place to yell at him, allowing Eggsy to watch the video transmission of the church events. This directly led to Eggsy realizing that Arthur was compromised and allowed him, Merlin and Roxy to take Valentine down before the evil plan was completed.
  • There were multiple spanners in Knives Out:
    • Ransom was the one to anonymously hire Blanc, assuming that his investigation will lead to Marta's incarceration as he was the one to tamper with Marta's medical bag hoping that it will result in Harlan's new will being nullified.
    • Marta ends up being this to Ransom's plan, as she was able to correctly identify the right medicine and never gave Harlan the fatal morphine dose.
    • Then there was Harlan himself who rather than let Marta get wrongfully indicted, constructs a complex plot to give her an alibi, forcing Ransom to adjust his plans.
    • Great-Nana is a spanner to Ransom and Marta's plans since she was the one to spot both of them climbing down the trellis on the night of Harlan's murder.
    • In the end, Blanc himself is the ultimate spanner, as he was the one to figure out that being anonymously hired to solve what appeared to be a suicide would be Too Good to Be True. In fact, the client would have to have ulterior motives when a large inheritance is on the line. He decides to take the time to solve the case and was able to discover the murderer.
  • In The Lady Vanishes, an oblivious Iris manages to completely destroy a Nazi conspiracy just because she won't give up insisting that the eponymous lady exists.
  • The ending of Layer Cake has the protagonist outclassed not by dumb luck, but by being shot. Because while he was really successful in tricking clever criminals in his Batman Gambit, he ends up shot (and possibly killed, it's a little vague) by a guy whose girlfriend he stole and whom he considered of little importance.
  • Convinced that everything is one giant reality-tv roleplaying game, Wallace in The Man Who Knew Too Little ends up convincing a veteran assassin to retire and dismantles a covert international plan to escalate the Cold War, saving god knows how many people in the process.
  • Mythica: The Iron Crown: Three different gangs of villains are chasing after the heroes, and any one of them could have succeeded if the others did not keep on getting in the way.
    1. Demons raised by the Big Bad Szorlok, who wants an item that the party have.
    2. Mercenaries hired by someone who thinks that he could do a better job than the party at keeping the item out of Szorlok's hands.
    3. A group of Sky Pirates led by The Admiral, who is just pissed off that the party stole her stuff and prevented her quiet enjoyment of her sex slaves.
  • Before both above films, you have New Jack City, where drug kingpin, Nino Brown, is able to fast talk his way out of serious prison time, only to get killed by an old war veteran he didn't take seriously during the film.
  • In Ocean's 11, all it takes is Anthony Burgdorf's widow deciding to have his funeral in Las Vegas for Operation Pine Box to go to hell.
  • Official Secrets: The Observer's front-page story revealing the US-British plot to influence the UN vote on the Iraq War is spoiled because a copyediting intern ran the story, including the reproduced memo, through spell-check, changing the American English spellings to British English. This is pretty close to what actually happened.
  • In One Foot in Hell, Mitch's plan to kill Dan and Julie probably would have worked if Dan hadn't disobeyed Mitch's orders and gone to town to tell Mitch that he and Julie had fallen in love. Because of this, he is at the sheriff's office when the Posse arrives back with the bodies of Stu and Ivers and immediately realises that Mitch has double-crossed them.
  • The Pink Panther
    • In The Pink Panther 2, it seems like Inspector Clouseau, a seemingly Inspector Oblivious, is one of these until the very end, where he reveals that he was a Chessmaster after all.
    • According to Peter Sellers, the original Clouseau qualified as well, but he knew he was a buffoon deep down.
    • The Pink Panther Strikes Again had killers from all over the world come after him. He bends over to tie his shoes at the exact right moment... Likewise in the film's Dénouement, Clouseau is unwittingly catapulted onto Dreyfus' Death Ray, destroying it and killing Dreyfus in the process.
  • All throughout Pirates of the Caribbean: The Curse of the Black Pearl, Jack repeatedly plots for the most favorable outcome (for himself), but stubborn fool Will Turner and arrogant jerkass Captain Barbossa assume they know best how to get things done, and nearly screw themselves out of their goals frequently. If Barbossa had wanted to cut Elizabeth's throat instead of her hand, Will would've been too late to save her on his own, and if Will had died like he should've when Barbossa ordered the Interceptor scuttled with Will trapped below, Barbossa would never have gotten Will's blood to pay Bill Turner's debt. Near the end of the film before the climactic battle, Jack has everybody where he wants them, but because Barbossa and Norrington don't trust him at all, his plans almost fall apart.
    • From the third movie, At World's End, it's Jack's turn to act as the Spanner which disrupts the East India Company's plan to wipe out the pirates at Shipwreck Cove. Faced with the imminent threat, the Brethren Court has gathered to choose a new pirate king; it's mentioned that this has happened many times in the past, but no king is ever chosen because every pirate inevitably votes for themselves, leaving the results tied at a single vote for everyone, preventing a new king from being chosen. Sure enough, as the vote goes around the table, every pirate puts in a vote for themselves...until Jack Sparrow casually votes for Elizabeth Swann, giving her two votes and thus the role of pirate king. As a result of her leadership, the East India Company (who came in expecting to massacre a bunch of unorganized pirates) instead found themselves facing an actual organized resistance.
  • The Downer Ending of The Pledge is triggered because some random idiot crashed with the car that the Serial Killer was driving to get to the trap the Cowboy Cop had set for him, killing him instantly. As a result, the killer is legally a Karma Houdini (until his own wife admits to his acts on a Deathbed Confession many years later) and the cop's life falls apart when his manipulations to set the trap are revealed.
  • Nicely played with in Quick Change. Grimm has carefully planned out a complex New York City bank robbery and it goes off without a hitch. He correctly anticipated just how the cops would react, how the hostages would behave and the exit strategy perfect. Grimm is just as confident the trio's plan to get through airport security and flee the country will also work. Sadly, Grimm never considers that getting to the airport is going to turn into a disaster...
    • The first problem is Grimm not knowing that the signs to a key expressway were removed during construction, leading to the trio getting lost in Brooklyn. From there, they're robbed themselves, a fire truck pushes their escape van down a hill, they run afoul of a mafioso and it just gets worse after that point. Amazingly, they do manage to escape but it's more sheer blind luck than anything they could have planned for.
  • Star Trek
    • Sulu in Star Trek (2009). By "leaving the parking brake on", he delays the Enterprise's warp to Vulcan, sparing the ship from the Narada's assault
    • Kirk in Star Trek Into Darkness. By threatening Harrison and offering him a chance to surrender, rather than killing him from afar as ordered, he single-handedly and accidentally derails all of Admiral Marcus' plans. And Spock, who drove him toward that decision.
  • Star Wars has a few examples:
    • Believe it or not, Valorum is this since before the films even chronologically began. Despite him being an ineffective leader, he was still a man with good intentions, and when the Senate didn't listen to him for too long, he decided to send the Jedi to negotiate with the Trade Federation without consulting with the senate, thus unwittingly planting the seeds for Palpatine's downfall.
    • The Ewoks in Return of the Jedi are the one tiny overlooked factor that brings the Emperor's entire grand scheme crashing down.
    • The Expanded Universe has the entire Imperial Fleet artificially boosted by the Emperor's force powers. The Emperor's death ended up causing the imperial officers to lose control of the situation, preventing them from shooting down the Millennium Falcon before it could destroy the Death Star 2.
    • There's also Jar Jar Binks, whose clumsiness is more than a match for several tanks.
    • There are about a dozen ways the Rebels lucked into the plans for the Death Star in the expanded universe. By now you'd think they had enough plans to spare.
    • Anakin Skywalker's destroying the Trade Federation's droid control station in the first prequel was a massive stroke of luck. To the extent that not even he realized what was happening. He just hid in an unmanned Naboo fighter and stuff happened.
    • Finn in The Force Awakens; his defection set the chain of events that would stop the First Order's plans. He frees Poe from them, finds Rey and BB-8, and helps them get off Jakku and meet up with the Resistance.
  • In Sudden Death, Foss has a great plan to use Game 7 of the Stanley Cup Finals to hold the Vice-President of the United States and others hostage to demand hundreds of millions of dollars in ransom. He's got bombs set around the arena, his men around it, explosives set to keep the cops at bay and the head of the Secret Service unit handling this is secretly on his side. All it takes for things to go awry is for the fire marshal's daughter to walk off and his trying to find her causing him to stumble onto the whole plot and fight the terrorists on his own.
  • Towards the end of Sunset Limousine, Alan decides to escape from the bad guys by blending in to a funeral procession at Inglewood Park Cemetery. As he and Julie are trying to figure out where in the chapel to hide from said bad guys, Alan accidentally triggers the incineration of the deceased, causing the mourners to file in. Luckily, the bad guys take the opportunity to flee the cemetery. Unluckily, they decide to do it in Alan's limo.
  • S.W.A.T.: Alex Montel kills his uncle Martin Gascoigne for sticking his hand in The Syndicate's till, then takes Gascoigne's car to the airport to catch his flight home. On the way, he's pulled over by a motorcycle policeman because he has a tail light out. The officer then discovers there's an arrest warrant linked to the license plate and detains Montel "until we can verify who you are." Lampshaded by an FBI agent after Montel's identity is discovered:
    "We've been lookin' for this guy a long time. Busted tail light brings him down? That's amazing."
    • This type of thing is very much Truth in Television, many real criminals are caught because of insignificant things that shouldn't have happened. One notable example is Timothy McVeigh, who was also caught when he was pulled over by a state trooper.
  • Sweeney Todd: The Demon Barber of Fleet Street: Sweeney Todd would have killed Judge Turpin and ended the movie right there and then in the middle had Anthony, who had recently talked to Sweeney about his plan to elope with Johanna in order to get her away from Turpin, not busted into his shop with the judge right there in the room in order to inform Sweeney that he has found Johanna and that she has agreed to the plan. Needless to say, this ends up blowing both the aforementioned plan and Sweeney's attempt to kill Turpin straight to hell.
  • In Thir13en Ghosts the housekeeper Maggie ends up discovering the mechanisms that run the "Ocularis Infernum" machine and begins hitting every switch she can grab, not only freeing the ghosts from the musical wail that imprisoned them, but also destroying the machine with the overloading.
  • The Hood's scheme in the infamous live-action Thunderbirds movie — to trap the Tracy family aboard the damaged Thunderbird 5 in orbit, invade Tracy Island to hijack the Thunderbird craft and then rob the biggest banks in the world, leaving International Rescue responsible — would've gone off without a hitch, had it not been for the presence of three kids (Alan Tracy, the youngest Tracy brother, Brains' son Fermat and Tin-Tin, the daughter of the housekeepers, and the Hood's niece), who then proceed to rescue the Tracys and help stop the Hood's plan.
  • In Tiger House, Kelly presence in the house was the one thing the gang had not bargained for.
  • In Under Siege, the bad guys have a brilliant plan to take over a battleship and sell its missiles on the black market. They neutralize the crew, have the Pentagon at bay and in total control. How were they supposed to know the cook was a highly trained NAVY Seal and the most capable warrior on the entire ship?
    • Likewise, in the sequel, Dane's entire plan would have worked out perfectly had he not chosen to use the exact same train Ryback just happened to be on.
  • Badass Bystander Gina in Unknown (2011). Despite just being his cab driver, she saves Dr. Harris' life at the beginning of the movie and twice afterwards, killing Mooks and the Big Bad in the process, which also allows Harris to stop the plan of the Big Bad.
  • The terrorists from Vantage Point might have gotten away with it, had it not been for a little girl.
  • The bank robbery in Violent Saturday probably would have gone off with a hitch if the robbers had picked anyone except Shelley's car to carjack.
  • In The Young Poisoner's Handbook, Graham's final mass poisoning attempt falls apart because management replaces the staff's individual mugs with a new set of identical ones, and Graham cannot keep track of whose mug is whose. And the irony here? Management got rid of the old mugs because Graham's previous poisonings made them think there was an infectious agent in the factory, and they were getting rid of possible sources.

    Music 
  • Invoked, if only as pastiche (which Morrissey adores, as we know) in The Smiths' title track "The Queen is Dead":
    So I broke into the Palace
    With a sponge and a rusty spanner
    • ...referencing a peculiar event—long forgotten by most, perhaps—though the unlikelihood of Michael Fagin's misadventure conveys this trope's inherent flavor of the unexpected. In the BBC's retrospective, we learn "[t]he Queen was only able to raise the alarm when he asked for a cigarette." In more security-conscious days, who'd imagine such a Royal contretemps could occur at all?

    Myths & Religion 
  • A conspiracy by Sejanus and Herod Antipas to overthrow High Priest Caiaphas and install Herod as King of Judea (a plot not mentioned in The Bible at all due to damnatio memoriae being inflicted on Sejanus), using Jesus of Nazareth as their pawn, ended in failure when Sejanus was brought up on murder and treason charges before the Roman Senate and sentenced to death by the garrote (resulting in the aforementioned damnatio memoriae), which resulted in everyone with even a remote connection feeling more vulnerable than ever, setting in motion the events leading up to Jesus's crucifixion.

    Podcasts 
  • The Black Jack Justice episode "Justice For Some" features a client of Jack's planning to steal his wife's heirloom necklace during an event and invite known thieves to be fall guys for Jack to catch. The plan fails because one had legitimately reformed, another was on a whole other floor casing the joint's artwork, and Jack managed to grab the third when the lights went out to facilitate the robbery. This leaves the client the only person in any position to have performed the act.
  • The Cool Kids Table Harry Potter-themed game Hogwarts: The New Class is built on this. The plan was to bring four American muggle-borns to Hogwarts and teach them magic in order to expand the wizarding community. Unfortunately, the four picked were four cloud-cuckoolanders who ignore almost all advice given to them and go out of their way to poke holes in every rule of wizarding society, causing McGonagall to quickly grow exasperated.
  • The Contention Boys in Pretending to Be People have little-to-no idea of what's going on, and have been known to fail so horribly that they wind up sitting on the ground, sobbing. They still managed to take out the head of one of the most powerful organizations in the series.

    Pro Wrestling 
  • In TNA, Taylor Wilde and Lauren Brooke derailed Dr. Stevie's attempts to turn Abyss into his puppet. Despite using drugs, physical abuse, and mind games to keep him in line, Dr. Stevie didn't count on Abyss falling in love with Lauren. Then, when he ordered Abyss to attack Wilde, he didn't count on her being Lauren's best friend...
  • Donovan Dijak was most responsible for bringing an end to The House Of Truth's second Ring of Honor run, the very same Dijak Truth Martini took in to prevent him from challenging for Jay Lethal's television title belt. He was paired with Joey Daddiego and redirected at the Tag Team titles of War Machine, but when he refused to use the Book Of Truth for an illegal advantage, Martini barred him from the group...and got kicked in the head as a result of this, allowing Prince Nana plenty of time to turn Dijak towards his own designs. Daddiego and Taeler Hendrix then went after Dijak and Nana in revenge, leaving Lethal basically on his own regarding Bullet Club, who swiftly positioned Adam Cole to take his last title belt.

    Roleplay 
  • It's extremely rare for this to not happen at least once per game in Comic Fury Werewolf. It also happens intentionally a surprising amount, considering.

    Tabletop Games 
  • In the Champions (5th edition) universe, the centuries-long, multi-dimensional, wheels-within-wheels master plan of DEMON's secret master involves in its final stages a literal Spanner in the Works. The precise timing that underlies the multiverse needs to be off just slightly for the rest of his plan to work and as such he has positioned a minion in the metaphysical boiler room of creation with a $10 hardware store spanner. Now he just needs the stars to align....
  • In Chrononauts, new players are the spanner. Plans in the game range from Gambit Roulette to "I win next turn as long as no one makes a minor change in 1914". New players will often meddle with history (even starting World War III), steal random historical artifacts, or kill the makers of said artifacts, to "see what happens".
  • Dungeons & Dragons:
    • In just about any D&D module, the adventurers are the Spanner. And any good GM has to be able to handle a Spanner, as the PCs can be expected to do the one thing the GM hasn't anticipated.
    • A mediocre GM can do this to players. When the players have a good plan which bypasses the intended challenge handily or solves a challenge with minimal fuss, a good GM may let the players have their moment in the sun and save those encounter notes to recycle them with new window dressing. A mediocre GM will have the players' plans fail for increasingly implausible reasons. A poor one will have a deer in headlights look as soon as the players are Off the Rails. Probably a good example of this is this story, where a player completely and utterly derailed a cynical GM's Crapsack World with Incorruptible Pure Pureness: in a game that had a Corruption Points mechanic representing how evil characters had become, his character singlehandedly defeated the Big Bad, took his Artifact of Doom, and used it on himself. Said artifact turned the user into a god at the cost of multiplying Corruption Points by 100. The GM declared he was now the new Big Bad, but the player revealed he had accumulated no corruption points at all, and 0 times anything is still 0. His character became a God of Good whose influence slowly made the Crapsack World less crappy over time.
    • Example: Give the PCs the Eye of Vecna, you get some fun people fighting over it. However, one of the PCs sacrificing the Eye of Vecna to THE GOD OF JUSTICE? Not so expected.
  • In Exalted, beings that exist outside of fate are the ultimate Spanners from the perspective of the Sidereals. Since they cannot be detected, manipulated, or predicted by fate and fate-based powers, one of these beings can derail centuries of careful planning before the Sidereals realize that anything's amiss.
  • In Unknown Armies, you can become an Avatar of an archetype by mimicking that archetype's classical behavior. One of those is The Fool, who can pull this off easily and walk away unscathed.
  • In Vampire: The Requiem, the Circle of the Crone has the position of The Fool, whose sole purpose is acting as this. When the Circle needs something stopped they send in The Fool and watch stuff blow up. Basically it's like "so, you're a rather spirited walking corpse, eh? Say, could you go check out what that Invictus bastard is doing downtown? Just do whatever feels natural, I'm sure it'll be a blast." Fools who survive long enough to gain some measure of respectability might make it to the rank of Trickster, for whom the purpose is basically the same except the Trickster actually has some idea of what he is doing.
  • Warhammer 40,000:
    • A common meme in Warhammer and Warhammer 40,000 is to label the defeat of Tzeentchian and Eldar forces as "Not as Planned"; as the smug bastards claim any victory is "Just as Planned". Of course, claiming the defeat was just as planned is a meme in itself...
    • During the 40K "Gathering Storm" event, Kairos Fateweaver succeeded in capturing the newly revived Roboutte Guilliman and his army as they made their way back to Terra, with the Lord of Change intending to torture the Primarch into crossing the Despair Event Horizon and joining Chaos. Before Kairos could really get started, though, the prison Guilliman and his forces were being held in was attacked by a massive horde of Khorne daemons led by Skarbrand, the Bloodthirster hoping to take Guilliman's head as an offering to the Blood God. The resulting Mêlée à Trois gave Guilliman enough time to rally his troops and escape to Terra.
  • In Eos games' Weapons of the Gods (an rpg based on a Hong Kong comic), one of the background stories of the world has an invincible martial artist invade the heavens. He's easily curbstomping all the gods in his quest for immortality, what stops him was this...he had an extremely stupid disciple that he's fond of nonetheless. The disciple complained that he was getting hungry, the martial artist decided that it'd be alright to take a lunch break so he sends the disciple off to go herb hunting while he slaughters some divine cattle. The disciple finds some chili peppers from the fields of the sun god and show them to his master. The master is pleased and makes a beef hotpot. Unfortunately as soon as he ate it, the peppers burned with the force of the sun and so he ran around screaming, eventually falling from the heavens to crash head-first into some rocks.

    Theatre 
  • Cyrano de Bergerac: Played hilariously straight: This play (a farce) has a lot of Gambit Pileup orchestrated by Cyrano, Roxane and De Guiche, but no one of them is capable of being an Unwitting Pawn for long.
    • Cyrano: Lampshaded by himself at Act II Scene VI: Unaware of it, he destroys De Guiche plan to set an arranged marriage with Roxane and De Valvert when he manipulates De Valvert to a duel.
      Cyrano: [bowing to Roxane]
      Then I fought, happy chance! sweet lady, not
      For my ill favor—but your favors fair!
    • De Guiche: When you apply Fridge Logic, you see that De Guiche was the Unwitting Instigator of Doom in his own plan to bully Roxane into a marriage with De Valvert at Act I Scene IV: When De Guiche makes a Dare to Be Badass to De Valvert, it’s only a small act, but it’s crucial because it sets a Disaster Dominoes scenario that ends with De Valvert being touched by Cyrano and so unable to marry Roxane. He also destroys his own plan to Buy Them Off Cyrano when he mentions that his uncle Richelieu could correct a line or two from Cyrano’s work.
  • The Yeomen of the Guard: Colonel Fairfax has been falsely accused of sorcery. In order to prevent his accusers from inheriting his property he marries Elsie Maynard so that she will inherit instead. When a plot to secretly rescue him succeeds he is honor bound to remain in the vicinity as he is now married.

    Visual Novels 
  • Ace Attorney:
    • The Big Bad's ultimate scheme in Apollo Justice: Ace Attorney ends up being exposed this way. Kristoph Gavin's scheme was meant to be the murder of Vera Misham via a poisoned postage stamp depicting the magician act Troupe Gramarye. However, the girl is such a huge fan of the Troupe that she saves the stamp for seven years; her father eventually uses the stamp instead and dies. The flaws in Gavin's plans run deeper than this, but this is his only apparent mistake; everything else is because of Phoenix Wright's meddling.
    • Larry Butz also counts, owing to his tendency to do unreasonable things that end with him stumbling onto vital evidence. In the first game, he was coincidentally returning a boat he had been using at precisely the right time to overhear a gunshot, in the third he shirked his work as a security guard when the villain's plan relied on him being at his post so that he would hear the noise of a panic button, rush into the room and arrest the wrong person and then in a later case his choice to wander around at night in the cold leads to him witnessing a number of things he wasn't meant to.
    • In the fourth case of Justice For All, the lead that helps Gumshoe and company track down Shelly de Killer is, of all things living and not living, Matt Engarde's cat, who meows at the end of a transmission from de Killer.
    • In the third case of Justice For All, Acro's plan to murder Regina was to call her to a specific point where he would drop a heavy weight on her head. Problem is, the note he secretly planted on Regina began with "To the murderer...". Due to Regina being very naive, she didn't think the note was for her, and posted it on the circus's bulletin board, where her father saw it and responded to it in Regina's place. Then you realize that Acro wanted to kill her because her naivete led to his brother being put into a coma, and he should have known that she would never realize the note was meant for her...
    • In Trials and Tribulations, Furio Tigre's plan to use Glen Elg's MC Bomber virus, worth several million dollars, to pay off his own million-dollar debt was annihilated because the moment the exchange was about to happen, Elg miraculously wins half a million in the lottery.
    • In the final case of Ace Attorney Investigations, the shenanigans of Larry Butz and Wendy Oldbag, of all people end up helping Miles Edgeworth put away the seemingly untouchable Big Bad. Larry, by accidentally breaking the Samurai Spear, forces the staff to have the Steel Samurai use a different move instead, thus enabling Edgeworth to realize that Alba was not at the Steel Samurai show while he was killing Manny Coachen. Wendy Oldbag takes the box of "Rising Sun Dogs," which turns out to have a drop of Alba's blood on it, and combined with Alba's wound, proves that he was injured while killing Coachen.
    • Larry gets to do this again in the manga. Simply by being arrested on suspicion of killing Bright Bonds (based on calling him and demanding that he get out of his ex-girlfriend's life), he derails the killer's plan to use him as an alibi, because she gets called in to prove his alibi, and through contradictions in her testimony, gets implicated as the murderer.
    • Phoenix Wright: Ace Attorney – Dual Destinies sees Phineas Filch end up as one in the second case. Florent L'Belle's entire scheme — a plot which took months of planning, backstabbing, manipulation, blackmail, threats, and outright murder, one so complicated that it's lampshaded how insanely complicated it all is by Apollo Justice — was all to have unrestricted access to the Forbidden Chamber in Nine-Tails Vale to steal a gold ingot supposedly contained inside of the Chamber. Filch, on the other hand, snuck into the Forbidden Chamber on a whim in fifteen minutes because he was bored. By doing so, Filch spooked Jinxie Tenma, which forced L'Belle to improvise a few things, proving to be his downfall in court.
    • Phoenix Wright: Ace Attorney – Spirit of Justice: The DLC case shows that Larry Butz's still got it; thanks to messily sneaking into a wedding reception because he was hopelessly infatuated with the bride, he not only screwed with the whole "time travel" theme and coverup that was attempted, his general interference also forced the culprit to enact his plan and murder his accomplice much earlier than intended, completely derailing everything and making it possible for the culprit to get caught.
    • In The Great Ace Attorney, Kazuma Asogi convinces Ryunosuke Naruhodo to accompany him on his study trip to London. However, Asogi ends up dying while on the ship, so Naruhodo takes a crash course in British law and becomes a lawyer in his stead. This throws a big spanner in Mael Stronghart's scheme, which was to have an assassin pose as an exchange student so they could benefit from Diplomatic Immunity. Now that another student showed up in Asogi's place and proved himself worthy of being on the study tour, Stronghart can't just send him back and look for another assassin without seeming very suspicious.
  • Danganronpa:
    • In Danganronpa: Trigger Happy Havoc, the entire triumph of hope over despair on Earth hinges on a poorly-fitting bathroom door that gets stuck in the doorframe. A door which, because of Naegi's Ultimate-level luck (which manifests as seemingly-bad luck that turns out to be good luck in disguise), gives him an alibi for a crime he would otherwise have been framed and executed for. Given how important Naegi would go on to be to the future of humanity, it's no exaggeration to say that that was the moment that Junko's fate was well and truly sealed. Even worse, it's implied that she deliberately gave him the crappy door just because the idea of the Ultimate Lucky Student being the only one with a crappy door was funny.
    • Naegi's luck is referred to as a "spanner in the works" verbatim by Junko; no matter how Crazy-Prepared she is for every possible scenario, Naegi's luck is totally unpredictable and can throw everything off on a dime, which is why she's captivated by him.
    • In the fourth chapter of Danganronpa 2: Goodbye Despair, Hajime is able to figure out who committed that chapter's murder because Fuyuhiko happened to wake up during the night and saw the victim heading downstairs, then sat down in the lounge and spaced out for a while. Fuyuhiko's presence in the lounge prevented the killer from returning to their room after carrying out their plan, and thus they couldn't secure their alibi of being fast asleep when their time-delayed murder method went off. Instead, the killer had to pretend they had left their room along with everyone else to investigate the ringing alarm clock in the lounge, which is proof they weren't in their room in the first place since they had one of the Deluxe rooms, which were completely soundproof.
  • In Hatoful Boyfriend's True Ending storyline, Dr Iwamine had won. Ryouta was mindless and implanted with the Charon Virus, Sakuya was emotionally broken, Yuuya and Hiyoko were both dead, and Kazuaki and Anghel were trapped. It takes two spanners to fix this. The first is Okosan, who snaps Sakuya out of his grief just in time to stop Anghel and Kazuaki from dying to nerve gas. This leads directly into the second — and most important — spanner, which is Anghel using his hallucinogenic pheromones to put Ryouta into a mental state where he could be talked down and prevented from wiping out humanity, thus unravelling everything Shuu had done up to that point. Needless to say, it's best not to fuck with the Joke Characters.
  • In Shall We Date?: Ninja Shadow, Makoto's route has his Anti-Villain brother Toru deploying an Evil Plan where he frames Makoto for murder to disband the Nagasaki Vigilantes, isolate his younger brother and force him to join his rebel cause. It works scaringly well despite Saori's efforts, until... Ukyo decides to call the Edo Vigilante group and ask them for help. The moment Kinshirou and Wakasa from the Edo group step in is the moment they strt working hard to learn what's going on, leading to them clearing Makoto's name and giving him and Saori the chance to confront, fight and capture Toru.
  • True Love Junai Monogatari:
    • The Player Character can potentially become this if following Ryouko Shimazaki's route. Ryouko is actually an Idol Singer (under the identity of Sonoko Takahashi) and has apparently retired, much to the sadness of her fans and the profit of her sponsors. Her manager and brother/parent figure, Tadaaki, actually had her fake her retirement to pique the interest of the fandom, then make the greatest come back ever — and since Ryouko is both his younger sister and his ward, she cannot stop him no matter how badly she wants to lead a life of her own. But after she befriends the MC, he inspires her to try speaking up and being her own self, leading her to rebel against the stage brother who controls her life and actions.
    • Also, if the PC pursues either Mayumi Kamijou or Yumi Matsumiya (who can't be romanced if at least a good part of Mayumi's path isn't unlocked first), he will also ruin Mikazaki's plan to blackmail Mayumi into sex and will give Yumi enough proof to get Mikazaki himself humiliated and kicked out of the school.

    Web Animation 
  • In the Homestar Runner holiday toon "A Death-Defying Decemberween," Homestar announces to one and all that he's going to sled down the Steep Deep — a vertical cliff face — and Strong Bad catches The Cheat surreptitiously helping Homestar bury a mattress at the foot of the alleged slope. Of course, Strong Bad being Strong Bad, he moves the mattress expecting Homestar to maim himself on impact...but the next day, when Homestar sleds down the Steep Deep, he makes a perfect landing. As it turned out, the mattress was full of "hammers, broken glass and candy canes sucked down 'til they're all pointy"; the whole thing was a ridiculously elaborate (and painful) scheme for Homestar to get out of having to spend Christmas with his girlfriend Marzipan's parents, one that Strong Bad successfully sabotaged (even if the end result wasn't quite what he had been expecting).
  • Red vs. Blue:
    • In Episode 100 of the Blood Gulch Chronicles (Seasons 1-5), Omega the evil AI has apparently won; He's repossessed Tex, captured Junior, Tucker's alien son, and has a ship to escape Blood Gulch with. What stops the computerized personification of rage from possessing Junior and using him to eventually take control of the aliens from within? The Red Team planting Andy the Bomb on the ship. This was originally done in an attempt to defeat the Blues, but Andy's presence allows them to blast Tex and Omega out of the sky, allowing Junior to escape in the chaos. On a smaller scale, Tucker finding the alien sword makes him immune to Agent Wyoming's time-rewinder, allowing him to remember the events of each iteration and eventually figure out how to stop the bounty hunter for good.
    • The Space Pirates from the Chorus Trilogy (Seasons 11-13) had a pretty good False Flag Operation; their leaders would play two rival factions on the planet against one another, fueling them with reversed engineered alien technology and special weapons from ships they forced to crash into Chorus using their tractor beam until both sides killed each other off, allowing their employers to take full control of the planet and all the alien relics therein. However, their last attempt was foiled when the ship tried to change course, jump to slipspace, and power down simultaneously, causing it to break apart on entry and leave some of its passengers alive. Said passengers are the Blood Gulch Crew, who not only complicated the attempted crash in the first place (purely by accident) but would also end up outing the Space Pirates scheme to Chorus and eventually the rest of the UNSC.
    • In Season 14, we learn how the Blood Gulch outposts were formed. Project Freelancer were going to use the place to hide the Alpha AI, so Agent Florida purposely assembled the worst soldiers from both the Red and Blue armies to fill the ranks, and even had a computerized personality (Vic) act as Command and keep both sides at a stalemate. Vic even had a roster of other Freelancers to recruit if anything happened to Florida. So what causes a perfectly orchestrated Forever War to spiral out of control, and eventually lead to the Project's destruction? Florida tripping over one of Vic's cables, then dying in a Stable Time Loop (Church tried to prevent his death by giving him aspirin, which he was allergic to). This scrambled Vic's systems and replaced the agents who were supposed to be sent to the teams with Caboose and Donut, whose Snipe Hunts (wait for an inspector with different armor than the Blue team and go to a store and get some elbow grease, respectively) end up with Donut running off with the Blue Flag. This caused Tex's appearance, Church's death, and ultimately the entire series.

    Webcomics 
  • Fighter of 8-Bit Theater is the living embodiment of this trope, as he's too stupid to know whether he's supposed to fall for a crazy plan or not. He bends the Theory of Narrative Causality by his very existence.
  • Antihero for Hire's Wizard lays it out cold for would-be Chessmaster Hector:
    You always overthink things. The reason your plans keep failing is not because your enemies are geniuses. It's because they are idiots. A plan is only truly foolproof if you consider the fool.
  • One of the characters in the Blip is this to God's master plan.
  • Obi-Wan and Qui-Gon end up doing this to Darth Maul in Darths & Droids. In a clever little inversion, this whole scenario is actually made up on the spot by the DM, after the events took place in which the players apparently screwed up everything by going Off the Rails. The author suggests this technique as a way of getting back at players who mess with your established scenario too much.
  • In Dead of Summer, the Big Bad's backup plan to blow everyone up with a Time Bomb was thwarted because Tito and Otis saved Panther, who proceeded to disarm the bomb and save everyone.
  • The majority of the plot of Demonology101 consists of Raven and her friends following this trope.
  • The main cast of Drowtales are Manipulative Bastards and Chessmasters whose plans often wind up crashing into each other, but so far the biggest example of this trope is Ragini, a child slave who survived the massacre at the Val'Sharess tower and was able to keep said Queen alive for a year, and then later become host to her aura and escape. If it weren't for her things in the story would be much, much different, and the full extent of her spanning potential is just beginning.
    • The Big Bad, Snadhya'rune, is implied to consider Ariel a key part of her plans. This results in the Big Bad's "Well Done, Son!" Guy attacking Ariel out of jealousy, ensuring Ariel will never trust the Big Bad.
  • I Don't Want This Kind of Hero: From Baek Morae's perspective, Haze ruined everything. Haze was a random trespasser who saved Raptor's younger brother, Stell, and uncovered the truth behind Baek Morae murdering all of her friends, therefore utterly destroying their relationship in the span of about a day. To rub salt in the wound, in the present day, he's the one who ended up with her.
  • Misfile: It turns out Rumisiel managed to throw a huge monkey wrench into a plot to destroy the Celestial Bureaucracy and remake the world and humanity by taking the key to his wing of the filing system with him when he got exiled, keeping it out of the wrong hands.
  • The Order of the Stick:
    • Roy Greenhilt qualifies for this in one early instance, despite being a very intelligent person, simply because he does something so very unexpected. Xykon honestly doesn't expect the heroes to stop him (and rightly so, as he has an army of monsters, 10 or more levels on the strongest PC, and a monster strong enough to send Paladins flying by LIGHTLY TAPPING THEM). He has three characters immobilized, two more being stalled by monsters, and he had JUST shattered the leader's ancestral sword. Confident that the battle is as good as over, he starts to call out the aforementioned monster to finish the heroes off. And then Roy goes and tosses his bony ass into a body-destroying Gate that holds an Eldritch Abomination at bay. The Big Bad is out of commission.
    • Elan is one of these for both the good and bad guys. Daigo at one point wonders if he's more useful the less he knows what's going on, and Durkon suggests that "He has Ignorance as a class power source." In 691, Roy lets him wander around the desert in the hopes that he'll stumble over something. WHICH HE DOES!
    • The unnamed Cleric of Loki restored Belkar exclusively because it would help him leave safely, which he immediately did. He had no interest in what Belkar did next.
  • Schlock Mercenary: In Book 15 Schlock ends up derailing a Staged Populist Uprising simply by drawing the attention of a police officer who was unwittingly carrying a bomb that was supposed to blow up the heads of the popularly elected legislature, providing the pretext for the fake revolt. And there was a second spanner- most of the police force was supposed to have their personalities overwritten as part of the uprising, it just that one of them was hijacked by a different party.
  • Sleepless Domain: Chapter 13 focuses on Rue fighting a monster, almost getting killed until Zoe steps in, choosing to battle for the very first time to save her. The chapter concludes with the reveal that the attack was staged by "The Purple One", the Big Bad of the story who has control over the monsters. The Purple One shows frustration that the attack failed even without the active interference of "The Golden One", who has occasionally led magical girls to places where they might be of aid. Zoe just happened to pick the right time to become brave.
  • In the Sluggy Freelance story arc "GOFOTRON Champion of the Universe," Zorgon Gola has a pretty nice Gambit set up where he pretends to be an Omnicidal Maniac, so that the heroes will sacrifice themselves trying to prevent a chain reaction that would destroy the universe, leaving him free to take over the Punyverse after their deaths. What he didn't count on was Torg, Riff, and Bun-Bun accidentally teleporting themselves into the Punyverse. They end up hijacking a vital piece of the heroes' Combining Mecha (the crotch). Without this, the heroes have no way of pulling off their Heroic Sacrifice, and Zorgon Gola, along with the rest of the Punyverse, is blown up. Oops.
  • In Season 9 of Survivor: Fan Characters, Prescilla/Bonnie has been controlling the entire game and has managed to take the two weakest players to the finals with her while tricking everybody into believing that she's just a sweet, innocent girl who couldn't POSSIBLY be an evil mastermind and gloats about how she has a 100% chance of winning the day just before the final Tribal Council. Then Cherman, the little robot who has been a Butt-Monkey for most of the game, reveals that he has a recorder he used to record Bonnie's Evil Gloating about how her only regret is that she didn't do more to hurt others. Your reign was nice while it lasted, Bonnie.
  • Quentyn Quinn in Tales of the Questor is a subversion. Instead of stupidity, it is a sense of honor and desire to help that make him accept quests which almost always indirectly monkey-wrench SOMEONE'S plans, generally without even knowing it. Examples:
    • A simple lack of knowledge led him to believe (and say) that human coins were forged. A politician's Oh, Crap! moment led a guard to realize they were indeed fakes—and who was behind it.
    • His very decision to become a Questor—paired with the discovery of an old contract—puts his home village in peril. The contract stated that the previous Questor was to retrieve some artifacts in exchange for land on which to build a village. The problem: the old Questor failed to do so, and now that there's a new Questor, a political faction intends to use that contract to get Freeman Downs repossessed and thus out of the picture. Quentyn's decision? Retrieve those artifacts, knowing that if he dies in the attempt, the law ensures that the contract ends with him. He knows nothing about the true scheme at work, and the opposing faction has no idea what to do now. The legal counsel sent to deliver the bad news summed this trope up rather perfectly:
    • His desire to help a human village ended with him in a position to UTTERLY screw over a fae—which he does so very EPICALLY. The fae in question calls a Wild Hunt on Quentyn, promising a wish if he survives. Quentyn barely manages to win, but it's now when the fae realizes to his horror that Quentyn is not only part of a race that's protected from the Hunt, but also under the protection of another being which doubly prohibits him. As punishment, the amount of wishes that the fae is supposed to give is tripled. The first two wishes are used to deprive him of everything he has. The third wish is a traditional "leave without taking revenge" wish...with an additional clause that forbids him from ever calling a hunt on that plane again.
    • And then there's Squidge, who is only too happy to prove that one can deliberately be this when he ruins Rahan's prank.

    Web Original 
  • Boomer, a Mad Bomber from the SCP Foundation storyline "Game Day", tends to carelessly leave dangerous explosives in random places around his hideout, to the point that it's not really possible to plan a safe approach to it.
    Boomer was the type to leave loads of bombs, traps and other assorted goodies laying around in a nightmare combination of cunning and blind, absentminded stupidity. You could plan around a smart enemy, a dumb one was prone to blowing your intelligent, well-planned ass off at random.
  • In the Whateley Universe, this is Jade's purpose in life. She's screwed over at least four plans, simply by being there. See "It's Good to be the don", "Christmas Elves", "Christmas Crisis", and Ayla 7-6.

    Web Videos 
  • Dragon Ball Z Abridged:
    • An odd variation occurs when Dende uses the last wish on Porunga to wish everyone off of Namek save for Frieza and Goku. Not only did this screw Frieza out of his immortality like in canon, but this was the same exact plan King Kai was going to use, only Dende beat King Kai to the punch and did it solely to piss off Frieza.
    • Earlier on, before Vegeta makes his way to Namek to gather its Dragon Balls, Cui tells him that Freeza heard about Vegeta's plans whilst he was on Earth, because the scouter was on the entire time. Vegeta is shocked at this, claiming the transmitter was off the entire time, but then he realises that Nappa was with him and probably forgot to turn off his scouter...
  • Double subverted during the Centralis battle in the Noob novels and webseries. Fantöm's plan was to distract Amaras simply by his unexpected presence to keep him away from the Coalition frontlines, depsite being much weaker than him. Amaras doesn't fall for it, but this is the time Spectre chooses to confirm the rumors about him being Back in the Saddle. The major difference is that Spectre is strong enough to give Amaras trouble and wants the Empire to win enough to keep him busy so it will have a chance. The novel version of scene mentions the trope by name.
  • When Tipping Forties LP'd Tales of Symphonia, they managed to go about 90 videos without using Presea, who they perceived as The Scrappy. The point was they hated the flatness of the character and refused to involve themselves with how stupid that part of the game was. Of course, they forgot the game was stupid (for that one instance, at least) and a scripted event forced them to use her. It nearly brought them to tears. Laser-Guided Karma.
  • In Ten Little Roosters, Chris just can't die, preventing Burnie from getting the killer four times in a row because he keeps acting like Boromir.
  • The "Heist" episodes of Achievement Hunter's Let's Play Grand Theft Auto V always have one that ruin their well thought-out robbery plans towards (usually) a convenience store.
    • The first episode "(Geoff's) Heist" gets derailed when their explosions causes their wanted level to hit 3-star, bringing in a helicopter.
    • "Gavin's Heist" goes bad when the explosives on the tanker truck they were using despawned due to distance.
    • "Ryan's Heist" got derailed due to just how much trouble the gang was having trying to get the Cargobob to the armored truck.
    • "Michael's Heist" hits a minor snag when he realizes that he can't rob banks yet (Rockstar hadn't added that in just yet), but recovers spectacularly.
    • "Jack's Heist" gets hit because of the escape jet they were using - they couldn't escape cleanly in traffic and later roasts Michael, who had the money.
    • "Ray's Heist" goes belly up because of a locked armored car door.
    • "The Grand Heist" stumbles at the finish line because the Titan stalled.
  • The first episode in the Persona Memeverse series ended with Haru completely trashing Atlus' headquarters because they wouldn't give her more screen time. The third episode reveals that FEMC used this to her advantage to escape the company's clutches, delaying their plans and kicking the series' plot into motion.
  • In Yu Yu Hakusho Abridged:
    Kurama: ...so I believe Hiei's superior speed would be the best choice for this fight.
    Hiei: Well Kurama, your plan sounds good except for one fatal flaw.
    Kurama: What? What are you talking about? My plan is foolproof!
    Kuwabara: [screen-shift] Here kitty kitty!
    Kurama: I stand corrected.

 
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Worried Mother

Being one of few Greenhorne residents who did not get their faces stolen, this allows the Worried Mother to give the player the antique charm which will release the guardian spirit and grant them the power to vanquish evil.

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