"A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools."Whether it's The Ditz, The Fool, Inspector Oblivious, or a monkey, this miscreant is capable of derailing the most ironclad plan by unknowingly taking a third option. 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. 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, they are an author's walking deconstruction or Lampshade Hanging of the Theory of Narrative Causality: just as easily as a plot can come together it can be pulled apart with the tiniest, most ridiculous things. These characters are The Chessmaster, Smug Snake, Manipulative Bastard, and Magnificent Bastard's worst nightmare. When the character ruins the protagonists' 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. Compare Finagle's Law, It Began with a Twist of Fate, Nice Job Fixing It, Villain, Outside-Context Villain, 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 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. Specialty of The Fool. See also Didn't See That Coming, The Dog Bites Back, Who's Laughing Now? The trope is reputedly named for the Industrial Revolution-era practice of disgruntled workers throwing a spanner into a machine, either because of fears 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. 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 plan.") 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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- 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..."
- 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.
- 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.
- 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.
- 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.
- 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.
- 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 lead 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 Mario Fan-Fic 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.
- Nanoha's presence in Game Theory (Fan Fic) 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
Films — Animated
- Oh, the joys of Chicken Run - this is one of many visual gags, and surprisingly one that is relevant to the plot.
- 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.
- Monsters, Inc.: According to Roz, Sulley and Mike were this to Waternoose's plan. She 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.
- Olaf was this. With Kristoff having left the castle when Anna was about to die, Hans' plan may have succeeded and given him the throne. But there was no way to account for Olaf, who saves Anna.
- Elsa was also this. Her denial of Anna's marriage to Hans and her departure from Arendelle wound up saving Anna as it delayed his plans and gave Anna a lesson in trusting people so quickly while at the same time showing her The Power of Love.
- In Home, Pig the cat's presence spared Tip from being abducted with the rest of the humans. When the Boov were collecting the humans, Pig panicked and clung to Tip's head. The scanner detected Pig instead of Tip and disregarded 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.
Films — Live-Action
- 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.
- 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.
- 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.
- Star Wars has a few examples:
- The Ewoks in Return of the Jedi are the one tiny overlooked factor that brings the Emperor's entire grand scheme crashing down.
- Luke just happens to wound Vader in the same way Vader wounded him, thus making Luke realize what he had almost become. Of course, the Emperor really wasn't helping his own cause, either.
- 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.
- 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.
- In the recent adaptation of The Pink Panther, 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. 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.
- 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 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.
- 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.
- That's what Jack WANTS you to think.
- 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.
- 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 The Man Who Knew Too Little the main character foils a terrorist plot without even knowing there was one.
- By refusing to sacrifice each other, the passengers on the two boats in The Dark Knight end up being this for The Joker, in that his social experiment in proving that anyone could be corrupted ends in failure.
- 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.
- The terrorists from Vantage Point might have gotten away with it, had it not been for a little girl.
- 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*
- 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.
- The Adjustment Bureau tries to contain this kind of incidents. But they are not above random chance and unexpected behavior.
- 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.
- 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, not because she is dumb, but be because she is clever enough to sense something in not right and thus goads Kaffee in doing his due diligence for once instead of rushing to a Plea Bargain, Dawson, for being too hardcore of a jarhead to willingly accept a dishonorable discharge because it would make thing easier for him, and telling Kaffee to take his plea bargain and shove it.
- 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.
- 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.
- 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 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.
- 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.
- 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.
- 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 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.
- 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.
- 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.
- In Ex Machina, Nathan underestimates just how much Kyoko can take in despite her lack of English skill or, more specifically, despite being an earlier model of artificial intelligence. This proves to be his undoing, as she grew resentful of his treatment and attempts to kill him - while her blow didn't immediately kill him, it gave Ava enough of an opening to finish the job.
- 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?
- 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.
- 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 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 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".
- 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 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.
- 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".
- In Tabletop Game/Champions 5th edition universe, The centuries long, multi-dimensional, wheels within wheels master plan of DEMON's secret master involves in it's 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 the metaphysical boiler room of creation with a $10 hardware store spanner. Now he just needs the stars to align....
- 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: (Bowing to Roxane):Then I fought, happy chance! sweet lady, notFor my ill favor—but your favors fair!
- 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.
- 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.
- Ace Attorney:
- Kristoph Gavin's ultimate scheme in Apollo Justice: Ace Attorney 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 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, which took months of planning, backstabbing, manipulation, blackmail, threats, and outright murder - so much so that it's lampshaded how how insanely complicated it all is by Apollo Justice - was all to have access to the Forbidden Chamber in Nine-Tails Vale to steal a gold ingot contained inside of it. Filch, on the other hand, snuck into the Forbidden Chamber on a whim in fifteen minutes because he was bored. By doing so, he spooked Jinxie Tenma enough and forced L'Belle to improvise a few things, proving to be his downfall in court.
- In Virtue's Last Reward, Dio aspires to be one for the AB Game. Too bad for him that not only is his presence expected, it is in fact required.
- The Player Character can potentially become this in True Love Junai Monogatari, 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 od 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 you don't finish Mayumi's path 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.
- 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).
- 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."
- The Space Pirates from the Chorus Trilogy of Red vs. Blue (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 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.
- 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.
- 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.
- And then there's Squidge, who is only too happy to prove that one can deliberately be this when he ruins Rahan's prank.
- 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.
- Roy Greenhilt of The Order of the Stick 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.
- 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.
- 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.
- One of the characters in the Blip is this to God's master plan.
- 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.
- A smaller version in Girl Genius —British spy/Gil's man Wooster just caused Dolokov's plan to corrupt/distract the Jaegergenerals while Wulfenbach forces destroy Castle Heterodyne to go thoroughly off the rails.
- 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.
- 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. And it was Hilarious.
- 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.
- 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.
- 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.
- 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.
- 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.
- An odd variation in Dragon Ball Z Abridged: 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 that Dende did it to piss off Frieza. Dende just beat King Kai to the punch.
- 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...