%% Image selected per Image Pickin' thread: http://tvtropes.org/pmwiki/posts.php?discussion=1399929864030086400
%% Please do not change or remove without starting a new thread.
[[quoteright:210:[[Webcomic/BugMartini http://static.tvtropes.org/pmwiki/pub/images/windex_in_doomsday_rocket_8134.png]]]]
[[caption-width-right:210:I wouldn't be too worried, [[BaitAndSwitch especially if that rocket's trajectory is set to strike my hometown.]]]]

->''"A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools."''
--> -- '''Creator/DouglasAdams''', ''Literature/MostlyHarmless''

Whether it's TheDitz, TheFool, InspectorOblivious, or a [[EverythingsBetterWithMonkeys monkey]], this miscreant is capable of derailing the most ironclad [[ThePlan plan]] by [[AchievementsInIgnorance unknowingly]] [[TakeAThirdOption taking a third option]]. They ruin the implausible {{Gambit Roulette}}s by [[FlawExploitation exploiting their one, intrinsic flaw:]] their reliance on {{Contrived Coincidence}}s, [[ClockKing rigid patterns]], and the assumption that nobody would be stupid enough to actually push the BigRedButton or fight the ''apparently'' [[NighInvulnerability unstoppable]] robot.

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

Put another way, they are an author's walking {{deconstruct|edTrope}}ion or LampshadeHanging of the TheoryOfNarrativeCausality: just as easily as a plot can come together, [[DidntSeeThatComing it can be pulled apart with the tiniest, most ridiculous things.]]

These characters are TheChessmaster, SmugSnake, ManipulativeBastard, and MagnificentBastard's worst nightmare, and the bane of many a ClockKing.

When the character ruins a {{protagonist}}'s plans by unknowingly doing something small but crucial, he becomes an UnwittingInstigatorOfDoom. When the Spanner can trigger a series of coincidences, it's DisasterDominoes. When the plan is screwed and the character is also aware that he will screw the plan, and doesn't care, he becomes a LeeroyJenkins. Occasionally, may be MistakenForBadass. If the focus isn't on them, they're often an UnknownCharacter.

Compare FinaglesLaw, ItBeganWithATwistOfFate, NiceJobFixingItVillain, OutsideContextProblem, RememberedTooLate.

Opposite of the UnwittingPawn, often ''is'' the UnwittingPawn until the final crucial moment. This is the main cause of DidntSeeThatComing, this trope being the "that". Quite often an [[AchievementsInIgnorance Achievement In Ignorance]]. Inverse of UnintentionalBackupPlan, where a character accidentally completes an imperfect plan that would have otherwise failed. Compare with OutGambitted, where someone's plan is successful but ineffective against a better-thought-out plan. Compare TooDumbToFool, where the character is too stupid even to be baffled by explanations. Also, compare EvilCannotComprehendGood, 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 TheFool. See also DidntSeeThatComing, TheDogBitesBack, WhosLaughingNow

The trope is reputedly named for the [[OlderThanRadio Industrial Revolution]]-era practice of disgruntled workers throwing a spanner into a machine, either because of fears [[JobStealingRobot machines would put them]] [[LuddWasRight 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|s}} 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.")

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.'''
* SpannerInTheWorks/AnimeAndManga
* SpannerInTheWorks/ComicBooks
* SpannerInTheWorks/{{Literature}}
* SpannerInTheWorks/LiveActionTV
* SpannerInTheWorks/RealLife
* SpannerInTheWorks/VideoGames
* SpannerInTheWorks/WesternAnimation


* ''Fanfic/TheChildOfLove'':
** 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 sonís 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..."''
* ''Fanfic/DoingItRightThisTime'': Asuka has grand ambitions to being this after realising she's in a PeggySue 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.
* ''VisualNovel/FateStayNight'''s fanfic [[http://www.fanfiction.net/s/6372400/1/Chaos_Theory# 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 [[IndyPloy 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.\\
[[SamaritanSyndrome You see, he really, really wanted to be a hero.]]"''
* ''Fanfic/{{HERZ}}'': SEELEís attack in 2015 failed because another secret organization accidentally learnt about their plans and interfered with themÖ something SEELE had not counted on at all.
* ''Fanfic/HigherLearning'': Gendoís plan started to unravel when [[spoiler:a teacher offered counseling to the Children]].
* In ''[[FanFic/UltimateSleepwalker 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 Franchise/SpiderMan 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 [[ShoutOut 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 VillainousBreakdown.
* The ''FanFic/PonyPOVSeries'' has one that's notable for the exceptionally long time required for the spanner to actually get into the villain's works. [[spoiler:Back in the G3 Universe, which was facing TheEndOfTheWorldAsWeKnowIt (actually a ShootTheDog 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? ''[[TheHero Twilight Sparkle!]]'']]
** During the [[BadFuture Dark World Arc]], [[spoiler: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 AnthropomorphicPersonification), mortally wounding him in the process. This ends up throwing a gigantic wrench in Nightmare Eclipse/Paradox's plans, allowing Discord to {{Out Gambit|ted}} her and alert Twilight to the [[GroundhogDayLoop true nature]] [[IronicHell 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 [[BigBad General-Admiral Makarov]]'s attempt to kill Shining Armor. Makarov ''[[WhoAreYou didn't even know his name]]'', yet he shows up [[BigDamnHeroes just in time]] to break through Makarov's AntiMagic field and save Shining. This also buys time for more Shining's forces to show up in a GunshipRescue 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. [[spoiler: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 [[spoiler: Shinji be aided by [[ItMakesSenseInContext 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 ''FanFic/ClashOfTheElements'', [[spoiler: 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 ''Fanfic/{{Game Theory|LyricalNanoha}}'' derails Precia's carefully laid plans. [[spoiler: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 ''Manga/FairyTail'' AU fic ''[[http://www.fanfiction.net/s/4711916/1/Lost-Magic 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 [[{{Irony}} Jellal, himself]]. [[ItMakesSenseInContext By accidentally getting himself pregnant with Erza's child.]]
* ''FanFic/JewelOfDarkness'': The only reason Midnight's plan to [[spoiler:torture Robin to insanity]] fails is because [[spoiler:[[MookLieutenant Ai]] [[TheStarscream betrays her]] on orders from [[GreaterScopeVillain Trigon]]]], something she ''couldn't'' have possibly anticipated.
* ''FanFic/QueenOfAllOni'': Jade's otherwise flawless [[OperationBlank 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 ''Fanfic/{{Kage}}'', Yua predicts [[WesternAnimation/JackieChanAdventures Jade's]] presence in [[{{WesternAnimation/WITCH}} Meridian]] will cause Nerissa's plans to go OffTheRails, 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.
* ''FanFic/AnAlternateKeitaroUrashima'' repeatedly derails his grandmother's attempts to manipulate him simply by letting others know how [[ManipulativeBitch 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 [[spoiler:some police officers are passing behind her and witness it]].
* ''Fanfic/DeathNoteEquestria'': Mer ends up [[TheStarscream going off Twilight's script]] in order to ruin her in revenge for [[spoiler: Rarity]]'s death as a part of one of Twilight's earlier gambits. [[spoiler: Subverted, however, as Twilight had actually anticipated this and factored it into her plans, resulting in Twilight's triumph and Mer's death.]]
* ''Fanfic/NedStarkLives'' reveals that Jaqen H'ghar had been hired by [[spoiler:the Great Other]] to kill [[spoiler:Jon]]. Arya's presence in the Night's Watch caravan completely derailed that plan, though.
* ''Fanfic/AHistoryOfMagic'': 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 [[spoiler: 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 ''Fanfic/TheVow'' (an AlternateUniverseFic of ''WesternAnimation/KungFuPanda2''), 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 [[NinjaMaid 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 ''[[http://www.tthfanfic.org/Story-20251-18/cmdruhura+We+re+Doomed.htm 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.
* ''FanFic/TheBridge'' gives a borderline humorous example in an otherwise completely serious situation. [[BigBad Bagan]] has set up an elaborate XanatosGambit that would work out in full to both secure more power for himself as well as kill [[BigGood 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 PhysicalGod got his plans set back by a photographer who didn't even know what she was snapping pictures of.
* ''Fanfic/{{Quicken}}'': [[AntiHero Emma]] accidentally and inadvertently causes a gang war only because she was in the wrong place in the wrong time wearing the wrong clothes.
* ''Fanfic/AdviceAndTrust'': Shinji and Asuka end up ruining Gendo's plans by [[DefusingTheTykeBomb 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.
* ''FanFic/ThisBites'':
** 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 RunningGag 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... [[spoiler: giving Blackbeard the perfect opportunity to swallow up his now-frozen opponents.]]
* Xander in ''[[https://www.tthfanfic.org/Story-28404-1/DianeCastle%2bXendra.htm 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.
* Ranma becomes one for not only Minaka and his Sekirei game in ''[[https://www.fanfiction.net/s/11701126/1/Anything-Goes-Game-Changer 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.
* In ''FanFic/CardcaptorRad'', the Decepticons plan to [[spoiler: invade the Autobot base]] actually ''works''. They likely would have succeeded in [[spoiler: attaining the Star Saber]] if not for [[spoiler: the humans and mini-cons being there]].
* In [[http://roosterteeth.com/user/CornOwl/albums/17723 this]] ''WebVideo/TenLittleRoosters'' fancomic series, every one of [[spoiler:Barbara]]'s attempts (and traps) to murder their Rooster Teeth colleagues [[HilarityEnsues is foiled due to the others' sheer dumb luck (with a few cases of taking a level in intelligence).]] The result? [[EveryoneLives Everyone ends up surviving]]:
** [[spoiler: Michael's poisoned glass]] breaks before they have a chance to [[spoiler: drink from it]].
** [[spoiler: Gavin and his clone]] manage to catch themselves, preventing them from [[spoiler: falling in the mousetraps]].
** ''None'' of [[spoiler: the arrows]] wind up hitting [[spoiler: Chris]].
** When reaching for the extra gun, [[spoiler: Burnie]] spots [[spoiler: the scorpian]] and shoots it.
** [[spoiler: Gus]] slams the door on the Killer.
** [[spoiler: Adam]] trips over a cord just as [[spoiler: the Killer is about to strangle them]].
** [[spoiler: The puma]] decides they're more interested in being [[spoiler: petted by Lindsay]] than [[spoiler: mauling her to death]].
** The part of [[spoiler: the treadmill]] that [[spoiler: Miles is glued to]] ''breaks off completely''.
* ''Fanfic/GuardiansWizardsAndKungFuFighters'':
** During the Battle of Torus Filney, the Rebellion's strategy hits a major stumbling block when [[LizardFolk 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 [[spoiler: [[SuperweaponSurprise they have guns]]]].
** Cedric and Wong's plot to [[TheStarscream betray Phobos]] and steal the Heart of Meridian from him catches [[TheChessmaster Nerissa]] completely off guard, throwing her own plans completely OffTheRails.
* In ''Manga/MyHeroAcademia'' fanfic ''Fanfic/ConversationsWithACryptid'', 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. [[spoiler: 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 [[spoiler: the Sludge Villain]] who proceeds to kidnap Midoriya, eventually resulting in [[spoiler: All For One breaking out of prison to rescue his son.]]

[[folder:Films -- Animated]]
* ''WesternAnimation/MyLittlePonyEquestriaGirls''
** In ''WesternAnimation/MyLittlePonyEquestriaGirlsRainbowRocks'', Sunset Shimmer proves to be this for the Sirens. Since she was immune to the Sirens' MindControlMusic, they instead opt to [[BreakThemByTalking break her will to rebel against them]] with a few well-placed {{Armor Piercing Question}}s and a HannibalLecture. While it briefly sends Sunset into a HeroicBSOD, Sunset still ends up rallying the Rainbooms together and gets them to break free from the Sirens' HatePlague.
** Spike has managed to do this twice. In ''Rainbow Rocks,'' after Sunset restores her friends' spirits, Spike has Vinyl Scratch free them from under the stage, allowing them to stop the Sirens at the concert. Then, in ''WesternAnimation/MyLittlePonyEquestriaGirlsFriendshipGames'', being Human Twilight's MoralityChain helps her briefly snap out of being DrunkOnTheDarkSide, allowing Sunset to break through the dark magic that corrupted her.
** Trixie becomes this in ''WesternAnimation/MyLittlePonyEquestriaGirlsForgottenFriendship''. Even though she's under the same LaserGuidedAmnesia the rest of CHS is hit with, Trixie sympathizes with Sunset's plight instead of hating her, and ends up becoming her NumberTwo. After the initial confrontation with the BigBad, Trixie also manages to get Sunset out of a locked room, letting Sunset confront the Big Bad again, this time where the other Equestria Girls can hear the culprit [[SayingTooMuch spell out their evil plan]] in a little too much detail.
* Oh, the joys of ''WesternAnimation/ChickenRun'' - this is one of many visual gags, and surprisingly one that is relevant to the plot.
* The title character of ''Disney/WreckItRalph''. His desire to gain the fame and respect his rival, Fix-It Felix, Jr., had, even unwittingly, lead to [[spoiler:''Sugar Rush'''s King Candy being exposed as the thought-dead Turbo and the restoration of glitch character Vanellope Von Schweetz]].
* ''WesternAnimation/MonstersInc'': Mike forgetting to file his paperwork, and Sulley volunteering to get it for him, end up causing a chain of events that [[spoiler: exposed Randall and Waternoose's plan]].[[spoiler: Roz]] gives them credit for exposing the scandal when [[ReverseMole she reveals her own true colors]].
-->'''[[spoiler: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 [[spoiler:Waternoose]].
* ''Disney/{{Frozen}}'':
** [[spoiler: Olaf]] was this. [[spoiler: 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 [[spoiler: Olaf, who saves Anna]].
** Elsa was also this. [[spoiler:Her refusal to give her blessing to 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 ThePowerOfLove.]]
* In ''WesternAnimation/{{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. [[spoiler:Were it not for this twist of fate, Earth and the Boov would likely have been destroyed]].
* ''Disney/{{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.
* Lord Farquaad in ''WesternAnimation/{{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 series.

[[folder:Films -- Live-Action]]
* The ending of ''Film/LayerCake'' has the protagonist outclassed not by dumb luck, but by [[spoiler:being shot]]. Because while he was really successful in tricking clever criminals in his BatmanGambit, he [[spoiler: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]].
* ''Film/CarlitosWay'' ends in a similar fashion. After outsmarting all his enemies by the skin of his teeth [[spoiler:Carlito ends up getting killed by some random lowlife he mistreated earlier in the film]].
* Before both above films, you have ''Film/NewJackCity'', where drug kingpin, Nino Brown, is able to fast talk his way out of serious prison time, only [[spoiler: to get killed by an old war veteran]] he didn't take seriously during the film.
* ''Franchise/StarWars'' 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 ''Film/ReturnOfTheJedi'' 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 [[WhatHaveIBecome almost become]]. Of course, [[http://www.irregularwebcomic.net/462.html 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 [[TheScrappy Jar Jar Binks]], whose clumsiness is more than a match for several ''tanks''.
** There are [[ContinuitySnarl about a dozen ways]] the Rebels lucked into the plans for the Death Star in the [[Franchise/StarWarsExpandedUniverse 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 ''Film/TheForceAwakens''; 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 ''Film/DialMForMurder'' 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 ''Film/GodzillaVsDestoroyah'', Godzilla spends days suffering a nuclear heart attack without even realizing it.
* ''Franchise/ThePinkPanther''
** In ''Film/ThePinkPanther2'', it seems like Inspector Clouseau, a seemingly InspectorOblivious, is one of these until the very end, where he reveals that he was a Chessmaster after all.
** According to Creator/PeterSellers, the original Clouseau qualified as well, but he knew he was a buffoon deep down.
** ''Film/ThePinkPantherStrikesAgain'' had killers from all over the world come after him. [[spoiler:He bends over to tie his shoes at the exact right moment...]] Likewise in the film's {{Denouement}}, [[spoiler: Clouseau is unwittingly catapulted onto Dreyfus' DeathRay, destroying it and killing Dreyfus in the process]].
* ''Film/SweeneyToddTheDemonBarberOfFleetStreet'': 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 ''Film/BigGame'', 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 ''Film/PiratesOfTheCaribbeanTheCurseOfTheBlackPearl'', 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 ''Film/DoctorX'' the MadScientist SerialKiller manages to not only [[spoiler:trick the other characters into believing he is innocent]] but also [[spoiler:manipulates them into physically restraining themselves so he can slaughter them at his leisure]]. Unfortunately he forgot about the PluckyComicRelief IntrepidReporter, [[spoiler:who manages to dispatch him in a terrified and bumbling fashion at the last minute]].
* In TheCaper film ''Film/TheKilling'', a band of criminals pull off an elaborate robbery of a racetrack. Even though the [[spoiler:most of the criminals kill each other off fighting amongst themselves]], the AntiHero and his {{Love Interest|s}} manage to [[spoiler: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 [[spoiler: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 ''Film/TheManWhoKnewTooLittle'' the main character foils a terrorist plot without even knowing there was one.
* ''Film/TheDarkKnightTrilogy'':
** In ''Film/BatmanBegins'', Batman himself is the Spanner towards [[spoiler: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 ''Film/TheDarkKnight'', in that his social experiment in proving that anyone could be corrupted ends in failure.
** And in ''Film/TheDarkKnightRises'', [[spoiler:Catwoman]] serves as one when [[spoiler:she saves Batman from Bane]] in the climax.
* In ''Film/CastADeadlySpell'', [[spoiler: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 ''Film/VantagePoint'' might have gotten away with it, had it not been for a ''little girl''.
* In ''Film/TheATeam'', [[spoiler: Face's plan]] would have gone off smoothly if not for [[spoiler: Pike having a [[http://en.wikipedia.org/wiki/Shoulder-launched_Multipurpose_Assault_Weapon SMAW]]]].
-->'''Pike''': Here's what I think of your best laid plans!
--> * Pike fires the SMAW into the ship's hull*
* CowboyCop [[Franchise/DieHard 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.
* ''Film/TheAdjustmentBureau'' tries to contain this kind of incidents. But they are not above random chance and unexpected behavior.
* BadassBystander Gina in ''Film/{{Unknown 2011}}''. Despite just being his cab driver, she saves Dr. Harris' life at the beginning of the movie and twice afterwards, [[spoiler:killing {{Mooks}} and the BigBad in the process,]] which also allows Harris to stop the plan of the BigBad.
* In ''Film/AFewGoodMen'', 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 PleaBargain 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 PleaBargain. Dawson, meanwhile, is too hardcore of a jarhead to [[HonorBeforeReason willingly accept a dishonorable discharge]] because it'd be easier for him, telling Kaffee to take his plea bargain and shove it.
* In ''Film/TheAtomicBrain'', as shown on the TV series ''Series/MysteryScienceTheater3000'', 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, [[EyeScream 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".
* ''Film/{{The Avengers|2012}}'':
** 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. [[spoiler: 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.]]
* Sulu in ''Film/StarTrek''. By "leaving the parking brake on", he delays the ''Enterprise''[='s=] warp to Vulcan, sparing the ship from the ''Narada''[='s=] assault
* Kirk in ''Film/StarTrekIntoDarkness''. [[spoiler: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.
* ''Film/ForrestGump'' calls to complain that he can't sleep because of people playing with flashlights in the next building over, and so [[HistoricalInJoke blows the lid on Watergate]].
* In ''Film/TheLadyVanishes'', an oblivious Iris manages to completely destroy a Nazi conspiracy just because she won't give up insisting that the eponymous lady exists.
* ''Film/{{SWAT}}'': [[BigBad Alex Montel]] kills his uncle Martin Gascoigne for sticking his hand in TheSyndicate'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." {{Lampshade|Hanging}}d 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 TruthInTelevision, 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 ''[[Film/{{Oceans 11}} Ocean's 11]]'', all it takes is [[spoiler:Anthony Burgdorf's widow deciding to have his funeral in Las Vegas]] for Operation [[spoiler:Pine Box]] to go to hell.
* This concept drives the entire plot for ''Film/DumbAndDumber''. 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:[[spoiler: 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 ObfuscatingStupidity, never understanding that no, they are actually that dumb, but happen to thwart the criminals at every turn.
* In ''Film/KingsmanTheSecretService'', 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 [[spoiler:Arthur was compromised and allowed him, Merlin and Roxy to take Valentine down before the evil plan was completed]].
* In ''Film/DayOfTheWolves'', #1's plan for TakingOverTheTown 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 ''Film/Thir13enGhosts'' 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 DownerEnding of ''Film/ThePledge'' is triggered because some random idiot crashed with the car that the SerialKiller was driving to get to the trap the CowboyCop had set for him, killing him instantly. As a result, the killer is legally a KarmaHoudini (until his own wife admits to his acts on a DeathbedConfession many years later) and the cop's life falls apart when his manipulations to set the trap are revealed.
* ''Film/ConAir'' features the AxCrazy 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.
* ''Film/{{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.
## Demons raised by the BigBad Szorlok, who wants an item that the party have.
## 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.
## A group of SkyPirates led by The Admiral, who is just pissed off that the party stole her stuff and prevented her quiet enjoyment of her sex slaves.
* 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.

* Invoked, if only as pastiche (which Morrissey ''adores'', as we know) in Music/TheSmiths' 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 [[http://news.bbc.co.uk/onthisday/hi/dates/stories/july/9/newsid_2498000/2498731.stm 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 [[FishOutOfWater contretemps]] could occur at all?

[[folder:Mythology and 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 [[{{Unperson}} 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. Since omnipotence and omniscience was the shtick of God in ''Literature/TheBible'', though, this may have been intentional.

[[folder:Professional Wrestling]]
* In ''Wrestling/{{TNA}}'', Wrestling/TaylorWilde and Lauren Brooke derailed [[Wrestling/StevieRichards 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 Taylor, 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 Wrestling/RingOfHonor run, the very same Dijak Truth Martini took in to prevent him from challenging for Wrestling/JayLethal's television title belt. He was paired with Joey Daddiego and redirected at the TagTeam titles of War Machine, but when he refused to used 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 Hendrix then went after Dijak and Nana in revenge, leaving Lethal basically on his own regarding Wrestling/BulletClub, who swiftly positioned Adam Cole to take his last title belt.[[/folder]]

[[folder:Tabletop Games]]
* In just about any [[TabletopGame/DungeonsAndDragons 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 [[OffTheRails 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 OffTheRails.
*** Probably a good example of this is [[https://i.imgur.com/qQ3j7MB.png this story]], where a player who played a BigGood in a CrapsackWorld completely and utterly derailed a cynical GM's world by being IncorruptiblePurePureness: [[spoiler:a game that had Corruption Points, his character had 0 and then obtained a special artifact that would make them a God but skyrocket their Corruption Points by a multiple of 100 to make them the new BigBad. However, 0 times anything is still 0]].
** 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 ''TabletopGame/UnknownArmies'', you can become an Avatar of [[CharactersAsDevice an archetype]] by mimicking that archetype's classical behavior. One of those is TheFool, who can pull this off easily and walk away unscathed.
* In ''TabletopGame/{{Chrononauts}}'', new players are the spanner. Plans in the game range from GambitRoulette 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 WorldWarIII''), steal random historical artifacts, or kill the makers of said artifacts, to "see what happens".
* In ''TabletopGame/{{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 ''TabletopGame/VampireTheRequiem'', the Circle of the Crone has the position of TheFool, whose sole purpose is acting as this. When the Circle needs something stopped they send in TheFool 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 [[TheTrickster 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 ''TabletopGame/{{Warhammer}}'' and ''TabletopGame/{{Warhammer 40000}}'' is to label the defeat of [[TheChessmaster Tzeentchian and Eldar forces]] as "Not As Planned"; as the smug bastards claim any victory is "[[AllAccordingToPlan Just As Planned]]".
* In the ''TabletopGame/{{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 metaphysical boiler room of creation with a $10 hardware store spanner. Now he just needs the stars to align....
* 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/CyranoDeBergerac: Played hilariously straight: This play (a farce) has a lot of GambitPileup orchestrated by [[TheProtagonist Cyrano]], [[LoveInterests Roxane]] and [[TheAntagonist De Guiche]], but no one of them is capable of being an UnwittingPawn 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 favoróbut your favors fair!
** De Guiche: When you apply FridgeLogic, you see that De Guiche was the UnwittingInstigatorOfDoom in his own plan to [[ArrangedMarriage bully Roxane into a marriage]] with [[TheBeard De Valvert]] at Act I Scene IV: When De Guiche makes a DareToBeBadass to De Valvert, itís only a small act, but itís crucial because it sets a DisasterDominoes scenario that ends with De Valvert being touched by Cyrano and so unable to marry Roxane. He also destroys his own plan to BuyThemOff Cyrano when he mentions that his uncle Richelieu could correct a line or two from Cyranoís work.

[[folder:Visual Novels]]
* ''Franchise/AceAttorney'':
** [[spoiler:Kristoph Gavin]]'s ultimate scheme in ''VisualNovel/ApolloJusticeAceAttorney'' was meant to be the murder of [[spoiler: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; [[spoiler:her father]] eventually uses the stamp instead and dies. The flaws in [[spoiler:Gavin]]'s plans run deeper than this, but this is his only apparent mistake; everything else is because of [[spoiler:Phoenix Wright]]'s meddling.
** Larry Butz also counts, owing to his tendency to do unreasonable things that end with him [[ShaggySearchTechnique stumbling onto vital evidence]]. In the first game, he [[spoiler:was coincidentally returning a boat he had been using at precisely the right time to overhear a gunshot]], in the third he [[spoiler: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 [[spoiler:wander around at night in the cold]] leads to him [[HeKnowsTooMuch 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, [[spoiler:Matt Engarde's ''cat'', who meows at the end of a transmission from de Killer]].
** In the third case of ''Justice For All'', [[spoiler: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 [[spoiler:Acro wanted to kill her because her naivete led to his brother being put into a coma, [[WhatAnIdiot 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 [[spoiler: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 [[NeverWinTheLottery wins half a million in the lottery]]]].
** In the final case of ''VisualNovel/AceAttorneyInvestigations'', the shenanigans of [[spoiler: Larry Butz and Wendy Oldbag, of all people]] end up helping Miles Edgeworth put away the seemingly untouchable BigBad. [[spoiler: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 [[spoiler: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]].
** ''VisualNovel/PhoenixWrightAceAttorneyDualDestinies'' sees Phineas Filch end up as one in the second case. [[spoiler: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 [[ComplexityAddiction 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.]]
** ''VisualNovel/PhoenixWrightAceAttorneySpiritOfJustice'': 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 [[spoiler: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]].
* The PlayerCharacter can potentially become this in VisualNovel/TrueLoveJunaiMonogatari, if following [[spoiler: Ryouko Shimazaki]]'s route. [[spoiler: Ryouko is actually an IdolSinger (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 [[PromotionToParent 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 [[IJustWantToBeNormal wants to lead a life of her own]]. But after she befriends the MC, he inspires her to try speaking up and [[BeYourself being her own self]], leading her to rebel against the [[StageMom stage brother]] who controls her life and actions]].
** Also, if the PC pursues [[spoiler: 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 [[spoiler: Mikazaki's plan to blackmail Mayumi into sex]] ''and'' will [[spoiler: give Yumi enough proof to get Mikazaki himself humiliated and kicked out of the school]].
* In ''VisualNovel/HatofulBoyfriend'''s TrueEnding storyline, Dr Iwamine had ''won''. [[spoiler: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 [[spoiler: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 [[spoiler: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 [[LethalJokeCharacter not to fuck]] with the {{Joke Character}}s.
* In ''[[VisualNovel/ShallWeDateNinjaShadow Shall We Date?: Ninja Shadow]]'', Makoto's route has [[spoiler: his AntiVillain brother Toru]] deploying an EvilPlan where he [[spoiler: 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... [[spoiler: 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 [[BattleCouple and Saori]] the chance to confront, fight and capture Toru.]]
* In the fourth chapter of ''VisualNovel/SuperDanganronpa2'', Hajime is able to figure out who committed that chapter's murder [[spoiler: because Fuyuhiko happened to wake up during the night and saw the victim heading to another floor of the building they were currently trapped in and decided to stay in the lounge in case they came back. 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.]]

[[folder:Web Animation]]
* In the ''WebAnimation/HomestarRunner'' holiday toon [[http://www.homestarrunner.com/xmas08.html "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 [[GranolaGirl Marzipan's]] parents, one that Strong Bad successfully sabotaged (even if the end result wasn't ''quite'' what he had been expecting).
* In ''WebVideo/YuYuHakushoAbridged'':
--> '''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.''"
* ''Machinima/RedVsBlue'':
** 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 FalseFlagOperation; 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 ForeverWar to spiral out of control, and eventually lead to the Project's destruction? Florida tripping over one of Vic's cables. This scrambled Vic's software, not only turning him into an idiot, but also replacing the roster with Caboose and Donut, the two soldiers whose respective {{Snipe Hunt}}s are the root cause of the Blood Gulch Crew's adventures.

[[folder:Web Comics]]
* In the ''Webcomic/SluggyFreelance'' story arc [[http://pics.sluggy.com/daily.php?date=010611 "GOFOTRON Champion of the Universe,"]] Zorgon Gola has a pretty nice [[BatmanGambit Gambit]] set up where he ''pretends'' to be an OmnicidalManiac, so that the heroes will sacrifice themselves trying to prevent a chain reaction that would destroy the universe, leaving him free to [[GalacticConqueror 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' CombiningMecha (the crotch). Without this, the heroes have no way of pulling off their HeroicSacrifice, and Zorgon Gola, along with the rest of the Punyverse, is blown up. [[MikeNelsonDestroyerOfWorlds Oops]].
* Obi-Wan and Qui-Gon end up doing this to [[spoiler:Darth Maul]] in ''Webcomic/DarthsAndDroids''. 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 OffTheRails. The author suggests this technique as a way of [[{{Railroading}} getting back at players who mess with your established scenario too much.]]
* Quentyn Quinn in ''Webcomic/TalesOfTheQuestor'' 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:
** [[ConvictionByCounterfactualClue A simple lack of knowledge]] led him to believe (and say) that human coins were forged. A politician's OhCrap moment led a guard to realize [[RightForTheWrongReasons 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:
---> ''"[[http://www.rhjunior.com/totq/00370.html Your Questor made a move they completely failed to prepare for. Unsurprising; I've found schemers and plotters are rarely able to cope with simple things like honor and courage.]]"''
** His desire to help a human village ended with him in a position to UTTERLY screw over a fae--[[GoodIsNotNice which he does]] so very EPICALLY. [[spoiler: The fae in question calls a WildHunt 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.
* Fighter of ''Webcomic/EightBitTheater'' is the living embodiment of this trope, as he's too [[TooDumbToLive stupid]] to know whether he's supposed to fall for a crazy plan or not. He bends the TheoryOfNarrativeCausality by his very existence.
* Roy Greenhilt of ''Webcomic/TheOrderOfTheStick'' 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 EldritchAbomination at bay. The BigBad is out of commission.
** [[IdiotHero 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 [[http://www.giantitp.com/comics/oots0558.html suggests]] that "He has Ignorance as a class power source." In [[http://www.giantitp.com/comics/oots0691.html 691,]] Roy lets him wander around the desert in the hopes that he'll stumble over something. [[http://www.giantitp.com/comics/oots0727.html WHICH HE DOES!]]
** The unnamed Cleric of Loki [[spoiler: restored Belkar]] exclusively because it would help him leave safely, which he immediately did. He had no interest in [[spoiler: what Belkar did [[http://www.giantitp.com/comics/oots0613.html next]]]].
* ''Webcomic/AntiheroForHire'''s [[http://www.antiheroforhire.com/d/20080317.html Wizard]] lays it out cold for would-be [[TheChessmaster 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 ''Webcomic/DeadOfSummer'', the BigBad's [[CrazyPrepared backup plan]] to blow everyone up with a TimeBomb was thwarted because [[spoiler: Tito and Otis saved [[Music/TheProtomen Panther]], who proceeded to disarm the bomb and save everyone.]]
* The majority of the plot of ''Webcomic/{{Demonology101}}'' consists of Raven and her friends following this trope.
* One of the characters in the ''Webcomic/{{Blip}}'' is this to [[spoiler: God's master plan]].
* The main cast of ''Webcomic/{{Drowtales}}'' are {{Manipulative Bastard}}s and [[TheChessmaster Chessmasters]] whose plans often wind up [[GambitPileup crashing into each other]], but so far the biggest example of this trope is [[spoiler: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 BigBad, [[spoiler:Snadhya'rune]], is implied to consider Ariel a key part of her plans. This results in the BigBad's WellDoneDaughterGirl attacking Ariel out of jealousy, ensuring Ariel will ''never'' trust the BigBad
* In Season 9 of ''Webcomic/SurvivorFanCharacters'', 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 [[BitchInSheepsClothing sweet, innocent girl who couldn't POSSIBLY be an evil mastermind]] and [[EvilGloating 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 ButtMonkey for most of the game, reveals that he has a recorder he used to record Bonnie's EvilGloating about how her only regret is that she didn't do more to hurt others. Your reign was nice while it lasted, Bonnie.

[[folder:Web Original]]
* When LetsPlay/TippingForties LP'd ''VideoGame/TalesOfSymphonia'', they managed to go about 90 videos without using Presea, who they perceived as TheScrappy. 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. [[LaserGuidedKarma And it was]] ''[[CrowningMomentOfFunny Hilarious]]''.
* In the ''Literature/WhateleyUniverse'', this is Jade's purpose in life. She's screwed over at least four [[ThePlan 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 ''Roleplay/ComicFuryWerewolf''. It also happens intentionally a surprising amount, considering.
* Boomer, a MadBomber from the Wiki/SCPFoundation 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 [[GeniusDitz 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 Creator/AchievementHunter's ''[[LetsPlay/AchievementHunterGrandTheftAutoSeries Let's Play Grand Theft Auto V]]'' always have one that ruin their well thought-out robbery plans [[spoiler: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 ([[DevelopmentHell 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 [[spoiler: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 ''WebVideo/TenLittleRoosters'', [[spoiler:Chris]] just can't ''die'', preventing Burnie from getting the killer ''four times in a row'' because he keeps acting like [[Film/TheLordOfTheRings Boromir]].
* An odd variation in ''WebVideo/DragonBallZAbridged'': 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 [[TheDitz Nappa]] was with him and probably forgot to turn off ''his'' scouter...
* Double subverted during the Centralis battle in the ''Franchise/{{Noob}}'' novels and webseries. [[spoiler:Fantöm]]'s plan was to distract [[TheAce 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 [[LivingLegend Spectre]] chooses to confirm the rumors about him being BackInTheSaddle. 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.
* The ''Podcast/BlackJackJustice'' 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.