!! Film - Animated
* ''WesternAnimation/BeeMovie'': Layton: "This is an unholy perversion of the balance of nature, Benson! You'll regret this." Needless to say, the defense attorney was absolutely right, as Benson's victory did upset the balance of nature. Fortunately, Benson did fix it before it became irreversible.
* ''Film/{{The Lorax}}'': The Once-ler starts off with good intentions when he makes the Thneeds, like not polluting the water, not clear-cutting everything, not consuming all the food, and not terraforming the forest into a wasteland. [[CrapsackWorld Now......]]
** Made even more significant when [[spoiler: he didn't have to chop all the trees down in the first place. All the harvesting was at the top meaning the wood wasn't needed at all, unless it was the material to build the industry.]]
* ''Disney/{{Mulan}}''
** Mulan's grandmother gives her a cricket to give her luck in order to help her with the matchmaker. While Mulan wasn't performing well to start with, it's obvious that the cricket ends up being a main direct cause for her failing the matchmaking.
** Compare the fate that would have awaited her if she had succeeded in her matchmaking with what happened after she failed. Had she succeeded, she almost certainly wouldn't have joined the army in her father's place, making it very likely that not only would he have died, the Huns would have managed to succeed in their invasion. She also would not have earned the respect of the Emperor or met and won the heart of Shang, who is a better match than the matchmaker could have arranged for her. Who said that cricket wasn't a lucky one?
** In the snow mountains, Mushu accidentally fires a rocket in the sky, revealing the heroes' locations to the Huns, which gives them some advantage in their fight. Good thing Mulan found a way to turn the tides to their favor...
* In ''WesternAnimation/{{Nine}}'', the title character's newfound friends [[spoiler: take out the mechanical beast who had been threatening them]], only for 9 to realize that [[spoiler:the MacGuffin he'd woken up with fit perfectly inside a larger machine nearby. Said machine proceeds to kill 2 immediately, followed by 8, 5, 6, and 1 before it's all done.]]
** Not only that, but what he did was ''exactly'' what said mechanical beastie was trying to do not five minutes before. TooDumbToLive.
** Also, the Stitchpunks [[spoiler:blowing up the factory]]. Beforehand [[spoiler:the Fabrication Machine had been SealedEvilInACan, being confined to said factory]]. However, instead of [[spoiler:being destroyed in the explosion, the Fabrication Machine was essentially freed, and proceeded chase after Stitchpunks itself, leading to the deaths of 5, 6, and 1]].
* ''Disney/WreckItRalph'': The Nicelanders' [[{{Jerkass}} behavior]] towards Ralph makes him leave the game to try to prove that he could be a good guy, which almost [[ApocalypseHow gets their game shut down]].
** Ralph's own game-hopping almost gets ''Sugar Rush'' devoured by a [[BigCreepyCrawlies horde of]] [[TheAssimilator Cy-bugs]], and turns BigBad [[spoiler:Turbo]] into a OneWingedAngel capable of taking down the whole arcade. The latter even calls him out, gloatingly thanking him for it. [[spoiler:He fixes both these mistakes by drowning them in lava.]]
* In ''WesternAnimation/KungFuPanda2'', if Po had not [[spoiler: entered [[EvilAlbino Lord Shen]]'s weapon foundry against the advice of Tigress]], then the [[FiveManBand Furious Five's]] plan to [[spoiler: blow up Lord Shen's cannons would have succeeded without a hitch. Instead, they had to get rid of their explosives or Po would be blown up along with [[BigBad Shen]] and the {{Mooks}}.]]
** And in the first movie Shifu, having seen Tai Lung's escape in a vision, send the goose Zeng to check and make sure Tai Lung's prison is secure. While there, Zeng accidentally drops a feather, which Tai Lung uses to pick the locks binding him and escape.
* In ''WesternAnimation/JusticeLeagueDoom'', Batman's CrazyPrepared status finally gets them into trouble when a team of villains decide to steal a bunch of data from his computer, specifically, the weaknesses of the entire Justice League.
--> '''Batman''': ''Alfred, get the Batwing ready! The Justice League is under attack!''
--> '''Alfred''': ''By whom?''
--> '''Batman''': ''By '''me!'''''
* Aladdin tricking Jafar into becoming a genie saved the day in ''Disney/{{Aladdin}}''. But when he gets loose in ''Disney/AladdinTheReturnOfJafar'', Aladdin's created a foe with all of the Genie's powers and none of the morals. Way to go, Al. Although at the same time, some of the threat is gone because genies can't kill, [[RunningGag but you'd be surprised at what you can live through.]]
* ''Disney/TheLittleMermaid'': Ariel's failed DealWithTheDevil causes her to allow Ursula to gain access to King Triton's trident, unintentionally dooming her civilization.
* ''Disney/TheLittleMermaidIIReturnToTheSea'': Ariel refusing to tell Melody about her merfolk heritage and her reason of not allowing her to explore the sea is what sets the plot in motion.
** Melody, for not handing over the trident to Ariel and giving it to Morgana.
* ''Disney/{{Frozen}}'': After Elsa accidentally struck Anna with her powers, their parents kept them apart and isolated her in her room; however, being isolated and fearing her powers is the reason Elsa can't control them.
** Anna, after she informs Elsa of the EndlessWinter she's created. The "breaking it" part is that she will not stop talking (how she's trying to help), which further drives Elsa into having a panic attack.
* ''WesternAnimation/ShrekFourD'': Fiona tosses a grappling hook at a rock in an attempt to stop the raft she's on from going over a waterfall, but when Shrek and Donkey show up to save her, they jump on the raft. The added weight causes the grappling hook to snap.

!!Film - Live Action
* At the end of the second ''Reiko the Zombie Shop'' movie adaptation, the title heroine confronts the bad guy who intends to resurrect the witch who was killed by Reiko in the first movie. The bad guy is at Reiko's mercy and she's armed with a dagger, so what do you think she does? Stab him? Wrong! She uses her trademark power to turn his victims (including a cop) into zombies who attacks the bad guy AND Reiko, then she grabs the zombie cop's gun and shot the bad guy to death, only to discover that by turning the victims into zombies, she also resurrected the witch who escaped while she was fighting. But wait, there's more: the last scene reveals that after Reiko left, the witch resurrected the bad guy and they are now working together. And guess what's worse? This cliffhanger is never resolved! The third and last movie adaptation deals about a different story, so we are left to assume that the two evildoers are still at large, thanks to Reiko being too dumb to use a dagger!
* At the end of ''Film/TheRing'', we find out that not only has the creepy girl from the well not been defeated, she's actually been released to reign terror upon the rest of the world. Plus she never sleeps, so it's not like we'll be getting a daily eight hour break from the reign of terror. Nice job, hero.
* In the American/Japanese science fiction/monster flick ''Film/TheGreenSlime'', the space station becomes infested with monsters made of the titular stuff because a visiting {{Jerkass}}/TheKirk had smashed on the ground an unauthorized sample of mold taken from an asteroid. He'd done this within a huddle of other astronauts, so naturally a fragment of the container (complete with a blop of slime) gets caught in one of the astronauts' pant-leg, and it naturally feeds on the radiation during the decontamination process.
* ''Film/JurassicPark'':
** After Nedry shuts down the fences to steal the embryos and make his escape, the TyrannosaurusRex gets out and wreaks havoc. In order to undo what Nedry has done, Hammond wants the computers shut down and restarted. When [[Creator/SamuelLJackson Ray Arnold]] initially refuses, Hammond insists: "People are dying. Would you ''please'' shut down the system." Arnold does so. Nedry was smart enough to program the raptor fences to stay operational during his sabotage; the total system shutdown releases the Velociraptors. Prior to this, the ''T. Rex'' had only killed one person and likely preferred snacking on its fellow dinosaurs as opposed to stringy, bony humans; the raptors kill two humans [[ForTheEvulz for the simple sport of it]], and relentlessly pursue the main characters for the rest of the film. Nice job, Hammond.
** When the ''T. rex'' breaks out and attacks the kids, Dr. Grant gets its attention with a flare and then throws it away, causing the ''T. rex'' to forget about the kids and chase after the flare. So far, so good, except Ian Malcolm tries to help with his own flare, which only causes the ''T. rex'''s attention to be turned back to the people instead of Grant's flare. Malcolm's own attempt to throw the flare away doesn't work because he's running while doing so, so the ''T. rex'' focuses on the larger moving target. The result is that it keeps chasing him, leading to Malcolm being injured and Gennaro killed.
** Also the [[DesignatedHero heroes]] of [[Film/TheLostWorldJurassicPark the sequel]], who are responsible for every single death in the entire movie.
* In ''Film/TheCabinInTheWoods'', when the heroes successfully stop the Evil Plan, they find the results [[spoiler:{{Eldritch Abomination}}s destroy the world without their once-a-year sacrifices]] fall under this trope.
* At the end of ''Film/{{Hellboy}}'', the titular AntiAntiChrist kills the villain [[RasputinTheMadMonk Rasputin]]... only for a ''very'' huge and scary tentacle monster to [[OneWingedAngel pop out of his dead body]]. Luckily, he manages to drive out the aboniation.
* In ''Film/{{Speed}}'', while under the bus in a failed attempt to disarm the bomb, Jack has to punch a hole in the bus's gas tank with his screwdriver as a makeshift grip to keep himself off the ground to avoid being run over when his cart breaks. By causing the leak, Jack has now significantly cut down the time he and the LAPD have in trying to find a solution to end the crisis. When he informs driver Annie about it once safely in the bus, she replies in a panic, "What, did you feel like you needed another challenge?!"
** Also, when the injured driver is being evacuated, the police on the flatbed try to get an old woman on the bus to come too, despite warnings from the bomber that he won't allow it. She [[spoiler:tries to leave, but a bomb is triggered beneath her feet, dropping her under the wheels of the bus.]]
* During the climax of ''Film/{{Dogma}}'', the fallen angel Bartleby needs to become human so he can take advantage of [[http://en.wikipedia.org/wiki/indulgence plenary indulgence]] in order to return to Heaven. Thus proving God wrong and thereby unmaking all of creation. To do so, he needs to remove his wings... which is promptly done for him with a machine gun by a particularly clueless hero who was trying to kill him.
* Every protagonist from the ''Franchise/{{Saw}}'' films (with the exception of ''Film/SawI'' and ''Film/SawVI'') suffers from this, the worst case being Matt Gibson from ''Film/Saw3D''.
* In ''Film/{{Immortals}}'', Theseus acquires the [[ChekhovsGun Epirus Bow]], but shortly after getting it, [[spoiler: he drops it. The weapon is then taken by a dog (don't ask) and delivered to the BigBad, who then uses it to ''great'' advantage. Had it not been for the gods' BigDamnHeroes moment at the end, his evil plans would've succeeded entirely.]]
* In ''Film/TheMatrixReloaded'', Neo encounters the Architect on his journey to destroy The Matrix. He learns that, if he proceeds, every man, woman, and child connected to the Matrix would die, which, combined with the destruction of the rebellion, would be TheEndOfTheWorldAsWeKnowIt. Neo does it anyway. It got better, though.
** By the way, Neo destroyed [[BigBad Agent Smith]] in the first movie; however, the latter came back as a rebellious program. Way to go, Neo.
*** We find from the final film, this was really a BatmanGambit by [[spoiler:The Oracle]], so Neo was filling his role exactly as intended.
* The film version of ''Film/HarryPotterAndTheOrderOfThePhoenix'' has a tragic example of this. Harry runs to his godfather's rescue [[spoiler:only to be the cause of Sirius's demise]]. [[FamousLastWords "Nice one, James."]].
* In ''Film/{{Frequency}}'', John manages to use the [[AppliedPhlebotinum time-travel radio]] to keep his father, Frank, from dying in the burning building that had claimed his life thirty years ago. And so doing began a chain of events that caused a SerialKiller to live instead of die who then goes on to murder many more women including John's mother. Oh, and did I mention Frank still dies from lung cancer because he smokes?
** The rest of the movie is spent trying to stop the serial killer from killing his other victims, including Frank's wife. [[spoiler:In the end, the killer, who is still at large in the present, breaks into John's house and attacks him while John's talking to his father on the radio. Right as it looks like he's going to win, in walks a thirty-year-older Frank with a shotgun. [[SugarWiki/CrowningMomentOfAwesome He'd heard the fight on the radio, and thus knew exactly where the killer was going to be thirty years from now]].]] Nice job ''fixing'' it, hero!
* The whole plot of ''Film/TheButterflyEffect'' is a series of these.
* ''Film/TheDarkKnightSaga'' by Creator/ChristopherNolan could almost codify this trope.
** In ''Film/BatmanBegins'', Bruce Wayne's desire for justice for Gotham leads him on a personal quest where he's declared dead, leaving Wayne Industries in the business of (among other things) weapons development. One device of Wayne Tech is stolen and used against the entire city. If Bruce had managed his company, that device might have never been made.
** ''Film/TheDarkKnight'': Franchise/{{Batman}}'s destruction of the Falcone family's dominance of Gotham City leads to not only a myriad of gangs trying to fill the gap, [[spoiler:but also the rise of SelfDemonstrating/TheJoker, who creates far more chaos and destruction.]] There are obvious real life parallels to international politics to when a power vacuum is created (collapse of the Soviet Union leading to rise of nationalism and fundamentalism) and law enforcement (the weakening of the Mafia that clears the way for Chinese, Russian, or Columbian gangs, for instance).
*** After Reese has run some numbers, Lucius Fox makes him do it all over again to teach him a lesson. This second, closer look leads to Reese discovering the identity of the Batman.
** ''Film/TheDarkKnightRises'': [[spoiler: Bruce Wayne dilly-dallies with nuclear fusion technology as an energy source, not realizing he was manipulated to do this to create a fusion bomb by remnants of the League of Shadows.]]
** Bruce choosing Miranda to be in take charge of the fusion reactor project, which grants her [[spoiler: the possibility of flooding the basement to completely give the heroes no chance of ever stopping the bomb in the first place.]]
** The whole plot of ''Film/TheDarkKnightRises'' is because Bruce "let Ducard/Ra's die" in ''Film/BatmanBegins''. [[spoiler:Talia, who used to have a rather strained relationship with her father prior to that, then seeks to accomplish her father's visions]].
* Happens in the '89 film ''Film/{{Batman}}'' as well with the Joker's backstory, though to be fair it really was an accident and Batsy [[ThouShallNotKill wasn't intentionally trying to push Jack Napier over the railing]]. Then again, this incarnation of Batman seems a bit more flexible with his code...
* ''Franchise/PlanetOfTheApes'': The original had an astronaut landing in the future from a freak accident. The [[Film/PlanetOfTheApes2001 remake]] has the hero CAUSING the freak accident that launches his ship even further back in time and giving his mutant lab apes free reign over a primitive world. Changes things considerably.
** ''Film/RiseOfThePlanetOfTheApes'' could have been called "Nice Job Breaking It Hero: TheMovie". [[spoiler: In his attempt to create an Alzheimer's cure, Will sets into motion the eventual dominance of the apes, as well as inadvertently creating the plague that wipes out most of humanity.]]
* Creator/JohnWoo's ''[[Film/BrokenArrow1996 Broken Arrow]]'' sees the hero finding a nuclear warhead which the villain has left in a mine. It hasn't been armed yet, so he comes up with the idea to enter the wrong arming code three times, causing a security measure to lock the warhead so it can't be armed. He does so...only for the villain to mockingly inform him that he used uncoded circuit boards, "You have just armed a nuclear warhead, my friend." Oops.
* At a fairly early point in ''Film/ReturnToOz,'' Dorothy mentions that the [[MacGuffin Ruby Slippers]] fell off her feet during her flight back to Kansas, and apparently thought nothing more of them after that. During the climax, the Nome King takes [[KickTheDog great delight in telling Dorothy what happened because of this]]:
-->'''Dorothy:''' My ruby slippers--\\
'''The Nome King:''' No, no, no... ''My'' ruby slippers. They just fell out of the sky one day -- you were so anxious to get home! They're very powerful: they made it possible for me to conquer the Emerald City... thank you.
* Near the end of ''The Haunting in Connecticut'', the reverend manages to exorcise the ghost from the house. [[spoiler: Too bad he's a benevolent spirit who was preventing the dozens of malicious ghosts from wreaking havoc.]]
* In ''The Monitors'', after the heroes drive off the dictatorial machines that enslaved mankind and stopped all human conflict, wars start breaking out all over the place.
* From the ''Film/JamesBond'' film ''Film/DiamondsAreForever'':
--->'''Tiffany''': I did it, I switched the tape in the machine.
--->'''Bond''': You stupid twit, you put the ''real'' one back in!
* In ''Film/FridayThe13thPartVIJasonLives'', Tommy Jarvis, [[NoKillLikeOverkill just to be absolutely sure]], digs up Jason Voorhees' corpse, and impales it with a steel rod. Cue [[LightningCanDoAnything freak lightning bolt]], which resurrects him as an unstoppable zombie.
* The FridgeLogic in ''Film/TenThousandBC'' sets in that, you know, D'leh and his buddies destroyed one of the only BASTIONS OF CIVILIZATION and set humanity back god knows how long. [[ValuesDissonance A few sacrifices isn't that much of a price to pay]].
* At the end of ''Annihilation: Earth'', David is torn between his idea of shutting down the particle colliders to stop the apocalypse or turning them UpToEleven, as his Middle Eastern colleague Raja suggests, which will (supposedly) force the anomaly to be "snuffed out." His boss makes him doubt Raja's motives, and David ends up going with his original plan. Cue the literal EarthShatteringKaboom. The moral of the story: not all Arabs are terrorists.
* ''[[Film/TheHungerGamesMockingjay The Hunger Games: Mockingjay Part 1]]'' has Katniss tearfully telling the cameras that the Capitol was responsible for the destruction of a hospital full of innocents. While the Capitol planes were showing aggression, it was actually Katniss and Gale who shot down the planes, causing them to smash into the hospital and completely destroy it.
* In ''Film/{{Dragonheart}}'', the knight Bowen is reluctant to kill Draco, even though it's the only way to save the kingdom from its AxCrazy king Einon, because Draco is the last dragon left in the world. Whose fault is that, might you ask? Why, Bowen's, who spent ten years on a personal crusade to wipe out the species!
** Eh, that was part of it, the other part being that Draco had become his best friend. See how eager you are to kill YOUR best friend when the chips are down. No, the real hero who did the breaking is Draco himself, by giving half his heart to a monomaniacal JerkAss he created an immortal dictator that made life a misery for his subjects.
** The Chinese in the sequel. First, they slaughter all their dragons because one of them turned out to be bad (whom the others immediately stopped and punished). Then they take the heart of the bad dragon to England, which results in the BigBad (the same dragon) restoring his original form.
* This trope kicks off ''{{Dracula}} Has Risen From His Grave'', in which a couple of priests go to Dracula's castle to exorcise any lingering evil left over from the previous Creator/ChristopherLee Dracula flick. One of the pair slips and falls on some rocks, and blood from his resulting scalp wound drips down to where Dracula's inert body is lying, reviving the vampire for another round of mayhem.
* ''Film/HeroicTrio'' sees an evil sorcerer kidnapping babies to raise as an evil army. One of the main characters kidnaps a baby in order to lure the real kidnapper out. This results in a fight between a fellow hero who [[LetsYouAndHimFight mistakes her for a villain]] and to make matters [[FromBadToWorse worse]], the real kidnapper shows up to fight both of them. The baby ends up dying in the process.
* ''Film/Tremors2Aftershocks'': While trying to escape shriekers, the 1st evolution stage of a graboid, they come across one in the way to an escape truck. So Burt Gummer, resident gun nut, whips out a {{BFG}} and blows it to [[LudicrousGibs bits.]] The problem? He was prepared to shoot at an underground creature, not the small above-ground shrieker. The bullet from the gun goes through the shrieker, a wall, several barrels of oil, and finally, the truck's engine. Burt's response? "How could I have known?!" [[note]]He ''couldn't'' have known. The shrieker was in front of a concrete wall.[[/note]]
* In ''Film/TheMummyTombOfTheDragonEmperor'', Lin, who had been the guardian of the tomb and tried to prevent the emperor from escaping, was responsible for knocking the diamond into the emperor that awakes him as she attempts to attack his decoy.
* In ''Film/TwentyEightDaysLater'', an AnimalWrongsGroup releases the Rage Virus when attempting to free some filthy monkeys. Keep in mind this is ''after'' they are directly told by ''a scientist'' that the monkey "is infected with 'rage' and all it takes is one bite".
* The rampant idiocy of the cast of ''Film/TwentyEightWeeksLater'' makes those guys look ''intelligent''. First the SwissCheeseSecurity of the compound allows people to leave the safe zone at will, leading to the discovery of a virus carrier that, [[WhatAnIdiot for some reason]], they bring into the safe zone and leave in an unlocked room with no guards to speak of. When someone inevitably gets infected, their "logical" decision is to herd the entire population into an poorly guarded room and shut all the lights off. Naturally, it gets worse when it leads to nearly everyone dead or infected. Then at the end, [[spoiler: the boy becomes a carrier and his sister [[TooDumbToLive neglects to ''tell'' anyone]], which results in the infection decimating France and possibly all of mainland Europe.]]
* In ''Film/{{Blade}}'', the hero doesn't kill Quin completely, allowing him to revive himself in a hospital to turn Karen and kill her boyfriend. Since Blade shows up immediately after this happens, looking for Quinn, he apparently knew that Quinn wasn't dead. His reasons for leaving Quinn alive in the first place are never explained, leaving a plot hole.
* ''Film/TransformersDarkOfTheMoon'': If Optimus Prime hadn't discovered the ''Ark'' on the moon, he wouldn't have been able to use the Matrix to revive Sentinel, allowing the traitor to kill Ironhide, steal back the Space Bridge Pillars, and join Megatron and work on enslaving humanity as a labor force to rebuild Cybertron.
---> Charlotte Mearing: (''After Sentinel ruins the NEST Base.'') ''"Yeah, take a good look, Optimus! This is all on you!"''
* In ''Film/{{Legend}}'', one of the "heroes", Lily, breaks it by [[spoiler: touching a unicorn, even after Jack tells her not to, resulting in the ice death of the world. It gets better. Eventually.]]
* In ''Film/{{Insidious}}'', the twist ending is revealed when [[spoiler:Elise takes Josh's photo, dooming herself and most likely Renai as well. On second thought, Josh is guilty of this as well.]]
* In ''Film/MemphisBelle'', the co-pilot begs for a chance to take some shots at the attacking German fighters, and is elated when he downs one of them ... only to watch in horror as it crashes straight into the tail of the rookie crew's bomber.
* In ''Film/IAmLegend'', Dr. Alice Kripin creates a mutated strain of the Measles virus which cures cancer ... and then promptly mutates again into a much worse virus that wipes out 90% of the human race and causes 99% of the survivors to be mutated into excessively violent vampire/zombie creatures which then slaughter all but a handful of the remaining uninfected people.
* The 2012 ''Film/TheThreeStooges'' film is about the trio trying to raise $830,000 their orphanage is in debt for. It's later revealed that they're in debt because of [[spoiler: insurance bills caused by injuries from their antics over the years]].
* In ''Recap/MysteryScienceTheater3000TheMovie'', Mike is goaded by Crow and Tom to pilot the Satellite of Love, despite being warned by Gypsy not to do so. Mike brushes her off, starts it off smoothly... then promptly runs into the Hubble Telescope. Then he tries to pull it off with the manipulator arms, tearing a part of it off wiping sweat off his forehead. When he finally releases, it suddenly drops to Earth as a fireball! Mike {{lampshade|Hanging}}s the improbability of the last one.
* ''Film/FlashGordon''
** Ming claims to only destroy planets that are advanced enough to realize his attacks aren't natural disasters...hence, it's Zarkov's own attempt to contact whoever was launching the attacks that nearly dooms the Earth.
** Zarkov also gets Flash killed. Good going. Flash [[OnlyMostlyDead gets better]] though.
* In ''Film/{{Skyfall}}'', M gave Silva to the Chinese to save 6 agents, but in the process caused Silva's StartOfDarkness, leading him to kill dozens of [=MI6=] staff later on.
** Q's attempt to decrypt Silva's computer by plugging it into MI6's network ends up [[spoiler: releasing a virus that opens every door in [=MI6=]'s new base, allowing Silva to escape.]]
* The fact-based drama ''Film/{{Amen}}'' about Kurt Gerstein, a member of the [[ThoseWackyNazis SS]] who develops and mass produces Zyklon B for use in Poland. [[MyGodWhatHaveIDone Then he finds out]] [[HeelRealization exactly what the SS meant by]] ''[[DeadlyEuphemism pest control]]''.
* Poor Marty [=McFly=] of ''Franchise/BackToTheFuture'' can't go one movie without doing this trope:
** [[Film/BackToTheFuture First film]]: Saves his dad from getting hit by a car--- which as a result keeps his parents from meeting, and in turn, is causing himself and his siblings to slowly be erased from existence.
** [[Film/BackToTheFuturePartII Second film]]: Purchases [[TimelineAlteringMacGuffin a sports almanac]]--- which {{Bi|gBad}}ff steals and delivers to his past self in 1955, allowing a new power hungry Biff to turn the post-1955 era into a BadFuture. And in another case of breaking things, Biff managed to use the Delorean to go back to the past just because Marty happened to be looking away from it for a few minutes.
** [[Film/BackToTheFuturePartIII Third film]]: Saves Doc Brown from getting killed by "Mad Dog" Tannen--- and now changes history so that he'll be the one getting killed instead.
* At the end of ''Film/{{Excision}}'', Pauline tries to [[spoiler:perform a lung transplant for her IllGirl sister Grace. It goes about as well as you can expect for a complicated procedure performed by someone with no medical training, little proper equipment, and a garage for an operating room.]]
* In ''Film/IronMan1'' Iron Man unintentionally causes the destruction of an Air Force F-22 that attempted to intercept him (before they knew he was a good guy). In his defense, he made sure that the pilot's ejection suit worked properly. Also, he helped to design and build many of the weapons being used by the Ten Rings (and presumably the Taliban, though that much is never stated in the first film).
* In ''Film/StarTrekIntoDarkness'', Kirk stuns a creature that appears before him as he runs from a planet's natives, only for Bones to tell him that the creature was their ride out.
** Furthermore, Kirk's lust for revenge is what ultimately [[spoiler:dooms the ''Enterprise'']]. If he had not desired vengeance against Harrison, there would have been no eventual confrontation with the ''Vengeance''. He wanted vengeance and he got it. [[spoiler:The ''Vengeance'''s merciless assault is what inspires his heartfelt apology to his crew, as seen in the trailer]].
** [[spoiler:Khan's decision to crash the ''Vengeance'' into San Francisco and kill countless innocents was probably influenced at least partly by the fact that Spock had tricked him into believing that all of his crew were killed]].
** Admiral Marcus points out briefly that landing in Klingon territory and taking out several patrols (even in self defense) will still draw the wrath of the Klingons against the Federation. [[spoiler:Even though this was his goal to begin with. It's implied this is the reason why the two are hostile to each other during the 5-year expedition of the ''Enterprise'', which starts at the end of the film]].
** As a furious Scotty points out, by confiscating his transwarp equation, Starfleet inadvertently ended up allowing [[spoiler: a rogue Starfleet officer to commit a terrorist attack and then jump across half the universe to safety]].
* [[Film/RevengeOfTheSith Yoda]] may have been a great military commander, but he sucked as an emotional counselor. In RealLife, it has been known since time immemorial that platitudes, no matter how well-meant, fall flat on the hurting. Unfortunately, platitudes were all Yoda had for a worried Anakin Skywalker. [[BigBad Darth Sidious]] promised actual help...
* ''Film/ManOfSteel'':
** When Clark tells Zod [[spoiler: how he managed to control his super-senses, Zod is able to make use of the information to become ''that much more dangerous''.]]
** When Clark begins exploring the [[spoiler: Kryptonian spacecraft he finds in the Artic, he inadvertently sets off a beacon that alerts Zod and his followers to the presence of Earth.]]
** Hell, pretty much ''every decision'' made by any Kryptonian who is not Zod in the opening sequence is an example of this: Jor-El stealing the codex, which did nothing but give Zod a reason to go looking for it. [[IllNeverTellYouWhatImTellingYou Jor-El telling Zod that Kal-El and the codex are on the rocket he just fired off]]. The council [[CruelMercy imprisoning Zod and his allies in the Phantom Zone]] when they know their planet is doomed, anyway.
* In ''Film/PacificRim'', [[spoiler: Newton drifts with a partial {{kaiju}} brain, and learns that the kaiju operate on a hive mind and are being engineered. Unfortunately, he forgot that the drift works both ways, meaning the kaiju hivemind now know what he knows.]]
** Also Stacker Pentecost grounding Gypsy Danger is what probably cost the lives of the two jaeger crews that died in the first double kaiju attack. If he had let the go out right away it's likely that all four of the last jaegers would have survived.
* In ''[[Film/PercyJacksonAndTheOlympians The Lightning Thief]]'', Percy slices off the Hydra's heads, not knowing that it would come back with ten instead of five.
* ''Film/{{Godzilla 2014}}'':
** The train carrying the nuclear warheads meant to take out the [=MUTO=]s is ambushed by a [=MUTO=], who promptly eats one of them.
** The Navy accidentally provoke Godzilla into destroy the Golden Gate Bridge.
** Godzilla stops the flying Muto with a quick tail swipe into a tall building...which then collapses on top of him.
* ''Film/TheDistinguishedGentleman'': The protagonist is a ConMan who's just scammed his way into Congress. The first time he votes, he doesn't even bother to find out what it's for, since he's having too much fun just being there. On a whim, he pushes "No". Then he encounters a public tour whose guide asks him about his vote and confronts him with the knowledge that it was a welfare bill. Oops.
* ''Film/ResidentEvil'': Alice and the assault team manages to shut down the Red Queen, only to realize that the Red Queen was attempting to contain the T-Virus infection within the Hive, and that they have now released hundreds of zombified animals and people into the facility.
* ''Film/TheWolfman2010'':
** [[spoiler:Gwen stops Aberline from shooting Lawrence, which in turn causes him to get bitten. However, this really doesn't do much good since Gwen ends up shooting Lawrence herself in the end. Although, she's somewhat justified since she was still convinced she could reach Lawrence, and well... [[IKnowYouAreInThereSomewhereFight she was right]]. Plus, she probably figured that Lawrence would have finished off Aberline instead of chasing after her instead.]]
** [[spoiler: Whilst in the Hindu Kush, the locals who told Sir John about the feral child in the cave, thus causing him to get infected.]]
* ''Film/XMen'':
** In ''Film/X2XMenUnited'', Rogue's impatience makes her indirectly responsible for Jean's death, due to crashing the Jet and causing the vertical takeoff to go temporarily offline. Furthermore, since the Jet appears to have been only about a few hundred metres from the facility, she really didn't need to fly to pick them up ''anyway''.
** Charles and Moira do this to each other in ''Film/XMenFirstClass'':
*** Moira desperately [[spoiler:shoots at Erik, forcing him to deflect the bullets, one of which paralyzes Charles right next to him.]]
*** Charles [[spoiler:erases Moira's memory, clearly discrediting her within the CIA and possibly ruining her career. The fact that one of the few snatches of memory she has left is of their kiss is just the icing on the cake.]]
*** Charles trains Erik, helping him improve his power. This backfires when he decides to turn into Magneto.
*** Had Charles [[spoiler: and Hank]] shown acceptance for Raven's true form, she might not have teamed up with Erik.
** ''Film/XMenDaysOfFuturePast'':
*** [[spoiler:Magneto tries to kill Mystique because experiments performed on her]] were used to give the future Sentinels their adaptive abilities. However, this attempt [[spoiler:spills her blood, allowing it to be collected and sent to Trask Industries]]. Subverted in that Trask [[spoiler:still needed the living specimen.]]
*** [[spoiler:The heroes' decision to break Magneto out ultimately does more harm than good. Given Mystique's reaction to Charles's presence, it seems leaving Erik in prison would have saved a lot of problems. It's even lampshaded by Xavier when he tells Logan, "It was a mistake freeing Erik."]]
*** Depending on how you interpret TheStinger, it seems that [[spoiler: in preventing the BadFuture, the X-Men have somehow inadvertently set the stage for Apocalypse to rise up and attack mankind in the new timeline]].
* ''Film/{{Transcendence}}'':
** It's made clear during the climax that [[spoiler: the AI was Will all along and all he wanted to do was fulfill his wife's dream of using technology to heal the planet. Had the Government not interfered, as well as Evelyn not give into her doubts, Will would have created paradise on earth. "Humans fear what they don't understand." Instead much of humanity is sent back to the Stone Age and countless millions likely died in process.]]
** Max actually sides with the people that murdered Will to stop the machine impersonating him. [[spoiler: They only succeed because RIFT threaten to kill Max unless Will destroys himself, a plan that only works because it's genuinely Will. Essentially Max enables RIFT to kill both his best friends and end a chance at a better world.]]
* In ''Film/StreetFighter'', we have Carlos Blanka who's been captured by [[BigBad M. Bison]] and what does Colonel Guile do? Tell good old Charlie to "hang on buddy" ''right in front of Bison!'' Way to tell the deranged lunatic who has a personal investment in you that he has your friend ''right there'' and at his mercy. [[MindRape Guess]] [[PlayingWithSyringes what]] [[BrainwashedAndCrazy Charlie's]] [[BioAugmentation fate]] [[WasOnceAMan is]].
* In ''Film/StVincent'', aside from hanging out with a prostitute, Vincent took Oliver to a racetrack and a bar while babysitting him. This ends up costing Oliverís mother half-custody when Oliverís father takes her to court.
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