Didn't Think This Through

"Mr. Krabs: Plankton! You knew I would never distrust a dollar! Plankton: That's right, Krabs! Now hand over the Krabby Patty secret formula! Beat Mr. Krabs: Or what? Plankton: I don't know. I never thought I'd get this far. Mr. Krabs: Well then, allow me to suggest your next move. [Mr. Krabs flushes Plankton down the toilet]"

- SpongeBob SquarePants

A situational trope. One character will develop a plan designed to solve a certain problem they're encountering. However, due to their failure to plan ahead, there is a massive gaping flaw in their plan that they, and also perhaps the audience, missed. As a result, they are now in a situation where, rather than winning, they are stuck with either a stalemate or an outright loss. As indicated by the page quote, this may occur because the character never thought that their plan would actually progress as far as it did in the first place.

A more comedic, simple version of Didn't See That Coming. If the person pointing this out is sufficiently annoyed, this can lead to What Were You Thinking?. Compare It Seemed Like a Good Idea At the Time.

Anime and Manga

 * At points in both the first and second seasons of Strike Witches, Minna pulls a gun on Mio in order to try to stop her from getting herself killed in battle. Mio is quite aware of the flaw in this bluff, and it doesn't work either time.
 * Vegeta during the Saiyan battle in Dragon Ball after Gohan turned into a Oozaru. Escaping being crushed multiple times, he did seem proud of himself for a moment after cutting off the boy's tail, thus shrinking him to normal size. Given that, while Vegeta has taken a considerable beating fighting the various heroes, Gohan was the last one strong enough to present any kind of threat to him, it seems that he's won. Then comes the brief realization that Gohan is still semi-gigantic, not maintaining his place in the air and now falling towards him while semi-gigantic. All of this happens in about a second, leaving Vegeta no time to dodge. Not long after a crushed Vegeta is sitting in a crater, struggling to crawl to his ship.
 * One Piece has the "Fake Straw Hat Pirates" based in Sabaody Archipelago after the time-skip. Since Monkey D. Luffy has attained even more infamy than ever before due to his part in the War at the Summit, One guy going by the name "Three Tongued" Demalo Black got the bright idea of posing as him and setting up a crew to pose as the Straw Hat Pirates, usually getting his way by relying on Luffy's fame to threaten people and recruit fearsome pirates into his crew. Unfortunately, round out the time they were recruiting the real Straw Hats came back, and it got steadily worse when they try to recruit a pair of Ax Crazy pirate captains who intend to kill the Straw Hats for more fame, and the Marines show up with Pacifistas, with a Marine Captain personally knocking out Demalo Black with his axe for trying to talk smack to him, while pretending to be Luffy.
 * Almost happens in Mahou Sensei Negima. The cast are discussing ways to retrieve Asuna and the Great Grandmaster Key from the Big Bads, and get the idea to use Natsumi's artifact (which makes the enemy completely unable to sense your presence) to get close for an ambush. Unfortunately  They almost go with the plan until Ako realizes the flaw. Cue Yue coming up with a workable solution, and a Crowning Moment of Awesome for everyone involved.

Comic Books

 * In the climax of Northwest Passage, Montclave reveals critical information to Simon in the hopes of permanently turning him against his father, Charles Lord.
 * Batman villain Warren "Great White Shark" White successfully pled insanity to escape embezzlement charges. He was sent to Arkham and wound up at the mercy of Gotham's worst psychopaths. Oops.
 * The Human Torch (not Johnny Storm, the original one) once fought a villain called Asbestos Lady, who figured the best way to fight a fire-based hero was by using an asbestos costume. Know how she died? From cancer. Go figure.

Film
"Dusty: We have a plan. Carmen: What is it? Dusty: First, we break into El Guapo's fortress. Carmen: And that you've done. Now what? Dusty: Well, we really didn't expect the first part of the plan to work, so we have no further plan. Sometimes you can overplan these things."
 * In Monty Python and the Holy Grail, when King Arthur's knights attempt to copy the Trojan Horse ploy with a giant wooden rabbit, none of them remember that they're supposed to get inside the rabbit until it's been taken into the castle.
 * Of course, given the French knights' predilection for catapulting just about everything they can find, actually getting into the rabbit would have been even worse.
 * This would also fit under Explain, Explain, Oh Crap.
 * Lampshaded in Three Amigos. Dusty Bottoms has found Carmen in her place of imprisonment.

"Genie: It's all part and parcel of the whole Genie gig. PHENOMENAL COSMIC POWER! ...Itty-bitty living space."
 * Hermione says this very thing to Harry in the Prisoner of Azkaban movie, when she saves their past selves from the werewolf...by luring it over to their current selves.
 * In Aladdin, Jafar is defeated when Aladdin tricks him into wishing to become an all-powerful genie. Jafar either forgot or was not aware that genies in this setting are bound to a magic lamp and obliged to grant wishes by nature.

""It's just, I have this big head, and little arms. I'm just not sure how well this plan was thought through!""
 * Gil's plan to escape to the sea in Finding Nemo which succeeds past the audience's expectations only to run into a snag at the end.
 * A Strange Minds Think Alike style gag in Meet the Robinsons often said to Bowler Hat Guy. When a CEO, a frog and a tyrannosaurus rex think your evil plans need work, you aren't doing that well.

"Let me get this straight. You think that your client, one of the wealthiest, most influential men on the planet, is secretly a vigilante who spends his nights beating criminals to a pulp with his bare hands. And your plan is to blackmail this person? ...Good luck. Beat ...Keep that..."
 * The Dark Knight Saga

"Crow: [as he causes the ship to suffer the wrath of space vacuum.] Oh, wow, this is confusing! Hey, Mike! Can you hand me my calculations? [paper flies into his mouth] Thank you! Oh, well, look at that: "Breach hull, all die!" Even had it underlined!"
 * The last line on Cloudy with a Chance of Meatballs, spoken by
 * In the DVD Commentary, the writers/directors lament that no one got the joke that this line was said immediately before the "Written and Directed by" credit showed up.
 * In Its a Boy Girl Thing Woody (in Nell's body) decides to get her a reputation for being easy. So he decides to have her sleep with this really sleazy guy. The Didn't Think This Through example occurs just before the deed is to be done when Woody realises that he is actually going to be the one to experience the drunken sex with a guy. Also counts as an Oh Crap moment.
 * Done hilariously in Mystery Science Theater 3000 The Movie with Crow's escape plan:

"Crow: Well, believe me, Mike, I calculated the odds of this succeeding against the odds I was doing something incredibly stupid and... I went ahead anyway."
 * Then lampshaded with his explaination:


 * In The Rundown, the sidekick's "Thunder and Lightning" attack never works. He becomes dumbfounded when it does work and needs a moment to think up the next stage of the attack.
 * In The Avengers: "Okay, we've got its attention... what was step two?"
 * In Waterworld, the villains' Evil Plan involves kidnapping a young child whose back is tattooed with some sort of runes that pinpoint the location of the last area of dry land in the world. They eventually succeed in grabbing her, only to find that, of the few of them who can even read, none of them has even the slightest idea how to decipher these runes.
 * In Monsters, Inc. prequel Monster University the Python Nu Kappa scare every single picture they find in the Scare Maze. Why did that backfire on them? Because according to the rules of the Scare Maze, they're only supposed to scare young children. If you scare enough teenagers, you'll be boxed in and will inevitably be eliminated from the Scare Games. This is exactly what happens to the sorority, who should have been more careful about who they scared.

Literature
"It was just at this moment that Bilbo suddenly discovered the weak point in his plan...Of course he was not in a barrel himself, nor was there anyone to pack him in, even if there had been a chance!"
 * The Hobbit: To enable the dwarves to escape from the Wood Elves, Bilbo secures them inside barrels so they can float away downriver. Unfortunately:


 * Not that being packed into a barrel himself would have been an improvement. Getting out again wouldn't have been easy.
 * Twice in Kitty Goes to Washington. Kitty had good reason to, but she didn't consider that this would mean   Later, Kitty tries to distract the guards on the first floor of a building by throwing rocks at the upstairs windows, hoping they'll investigate the crash. She realizes belatedly that if they instead put two and two together and look out on the street, she'll get caught red-handed. (Luckily, they're typical guards.)
 * In the Knight and Rogue Series, when told he must, in order to regain his legal rights, capture a murder suspect he released from jail and become his brother's steward, Michael sets out to bring the criminal to justice. Upon learning he decides to not even bother with bringing her to trial, opting to be tattooed as a horible criminal instead. It's not until afterward that he realizes this will make people hate him by default and take advantage of him due to his being unable to go to the law for help. Bonus points for his father forcing the situation on him in the hopes that only his oldest son will hire Michael for a stable job if he's marked, as he apparently didn't notice that Michael spent the whole past year funding his adventures by stopping for the day in random towns and doing odd jobs for people who don't need to see the area on his arm where he gets marked.
 * In Monster Hunter International Siege a lawyer (who is a Contest Winner Cameo) steals an important file from under the protagonist's noses and, thinking they work for the mafia, tries to blackmail them for it. His attempt is the worst blackmail possible. He sets up a meeting in person in front of his work place so the people supposedly being blackmailed just need to look at his employer's website to find his real name and share his face with their comrades. He sets up this meeting in a seedy bar downtown... while still looking like a successful lawyer and standing out to a crazy degree. Despite having seen how blatantly huge Owen Pitt, one of the people he attempts to blackmail, is and believing they work for the mafia, is totally unprepared for the possibility of physical threat. When a third party enters and threatens him, he still hasn't learned his lesson and starts from the top. When the protagonists effortlessly dispatch the third party with firearms and tell him they were a zombie and some necromancers, he still tries to go through with the blackmail before finally admitting he kept the file on his person. Owen Pitt dubs him the "worst blackmailer ever".

Live Action TV
"Tarrant: I hadn't really considered it. Vila: What? Tarrant: I thought we'd be dead by now."
 * An episode of Blake's 7 plays this for laughs with its justification: when Vila asks Tarrant if he can actually dock their tiny ship into the Liberator that they have just reclaimed from Servalan, the following exchange occurs. (Incidentally, it's just a throwaway gag, since the very next scene has them already back on the Liberator safely.)


 * In Buffy the Vampire Slayer, Spike schemes to both break up the Scooby Gang and plant evidence to lead Buffy into a trap. It takes the Big Bad he's working for to point out that he's given Willow the evidence, and Willow won't be speaking to Buffy now.
 * In a Saved by the Bell episode, Zack has detention on the day of a trivia contest for a trip to Hawaii. He send's Screech in his place, who comes back to ask him a question. Mr. Belding explains only those in detention can talk to others there, so Screech purposely gets in trouble. When he sits down, Zack tells him the obvious problem with that plan.
 * On an episode of Seinfeld Kramer is at a department store when he decides to sell the clothes he's wearing to another customer. When he's left naked in the store's changing room with nothing to put on, he whimpers, "I didn't think it through!"
 * Kramer does this kind of stuff a LOT. Like betting that he would turn his apartment into a triple tiered deck.
 * A amphibious car challenge, Hammond's car looked like a boat (with the steering wheel near the back) with an upper portion for the "girls in bikini to go," which he then noticed was so high up he couldn't see over while driving.
 * In th Doctor Who double episode "Aliens of London"/"World War Three", Slitheens get into Downing Square 10, and chase (the Ninth) Doctor, Rose and Harriet Jones. The Doctor activates a defence mechanism that means there is 5 cms of thick metal between them and the Slitheens - or any way of escape. "There's no way they can get through." "And how are WE going to get OUT?" ... "Oh."

Music

 * Have you heard the story of Bottleneck Bob? He tried to rob the train with cattle, but evidently forgot they needed to be corralled somehow: "The cattle ran all over the place / And there was Bob with the longest face"

Newspaper Comics

 * This Dilbert strip.

Video Games
"Draenei Male: Step one, we land the Exodar. Step three, we defeat Legion and go home. There is only one detail missing...."
 * A frequent experience in Bomberman: Place bomb, walk into alley, realize alley is a dead end because of said bomb...
 * World of Warcraft:


 * In Kingdom Hearts: Chain of Memories, Larxene is trying to cheer Namine up about the plan. Namine replies that they want part of Kairi to replace Kairi in Sora's memories so that he'll forget Kairi. Spot the flaw in this plan.
 * Something you can do in Smackdown vs Raw 2011 ladder matches. Have you and your partner both climb up a ladder. The opponents get up and realize they could just tip the ladder over. Cue doing just that.

Web Comics
"Female Immortal: I hate being invisible and intangible; it feels like cheating. Male Immortal: We can't exactly claim to be "everyday students" and expect to pass unnoticed in Elliot's house. Female Immortal: We could pretend to be burglars! That would make sense, right? Male Immortal: ... I don't think you've thought this through..."
 * An early strip of Sluggy Freelance starts off with Riff and Torg talking about how Zoe has a date with this guy she has a huge crush on. Riff then mentions that he is going to visit his ex-girlfriend Gwynn at her apartment, which she shares with Zoe. Torg is surprised that Riff going to see her alone like that. Riff insists that they're not alone, that Zoe will be there...at which point he realizes that even though he was aware of both of these pieces of information he only just now realized that they were related.
 * Referenced in El Goonish Shive, but averted by discussing the plan before trying it, allowing someone else to point out the flaw ahead of time.

": Every properly trained wizard has heard of Abraham, the idiot apprentice who recklessly enchanted a massive diamond instead of selling it to pay someone more skilled to fix his cursed noble friend."
 * Abraham. Almost everything he ever did and we know about.

"Fontes: ...I really shouldn't have made him able to summon firearms..."
 * He claims trying everything he could to destroy it after it Gone Horribly Wrong. Only to be immediately asked whether he tried to chuck it into a volcano - c'mon, this didn't occur to him? Even if it would not burn, at least would be harder to reach.
 * And he swore to destroy every creature created by his botched enchantment on the assumption that the Dewitchery Diamond would be used against curses (like his werewolf friend), thus creating monsters. He hadn't accounted for the Diamond being used to rid people of harmless, if annoying, magical conditions - this guy clearly didn't have much classic education or curse lore, if he never heard of - or that the botched artifact's criteria of "curses" can be vague enough to include cosmetic magic (which was obviously bound to happen - and did, to the second DD's "victim" shown).
 * Webcomic/webgame Wicked Awesome Adventure points out how often this befalls adventurers in the course of escape and exploration.
 * J.E.T. enlists the help of a wounded and unwilling Candimp to disarm a trap.
 * Rhys solves a puzzle to access a new area of the Haunted House for exploration- opening a trap door, too.
 * Girl Genius got a few examples. Like this guy.
 * This appropriately titled Order of the Stick strip.
 * Fontes' Rants: Fontes uses the Life Note, a Parody of the Death Note which creates a life form he writes in it, to create an Ax Crazy Marty Stu character. When he recovers after inevitably being knocked out;

"The Anarch: I may have made a slight error in my calculations. Punchline: When you were adding up the numbers, did you remember to carry the stupid? The Anarch: Yes! ...no."
 * From Super Stupor, this strip, after Punchline explains why The Anarch's plan is really just Suicide by Superhero:

"Kerchak: And Then What? Breya: I...haven't thought that far ahead. Kerchak: I'll bet you a bushel of pureed bananas he has."
 * In Schlock Mercenary, the UNS tries to use a court case to capture under a good-looking pretext the company that accidentally acquired illegal (and as it turned out later, also scandalously secret) military/medical technology. A nearly-all-powerful AI plainly states that it's not a question whether they have it. They do. The real question is - do UNS want ? Then they try to use this opportunity to trick said godlike AI into admitting that he has been performing morally questionable actions (specifically, "disappearing" problematic people).

"Ebbirnoth: Doesn't that path lead right back to you? Murtaugh: Give me a moment. I really want for this to be a good idea..."
 * Kevyn's plan to install sneaky hardware under pretence of containing particularly obnoxious nanobots. Tagon asks the obvious question.
 * Schlock was left behind when the team gone outside on an airless planetoid because he haven't Powered Armor. Then he noticed EVA suits rack... "Sergeant Schlock poured himself into an emergency exosuit and jumped into a 6200 meter deep excavation. Local acceleration is 9.114 m/s2. This exosuit has no flight system."
 * Ebbirnoth wanted to check whether Elf is mentally stable... during an emergency. He admits his plan was flawed.
 * Murtaugh wanted to short-circuit stormy atmospheric layers using her plasma gun.

"- You do realize you've just killed both of us, right? - Oh, dear, you didn't allot me enough of processing power to see that coming."
 * A copy of crazy AI running on hardware controlled by another AI pulled the old "Help, I'm trapped in fortune cookie factory" trick. The host points out that this simply means it's known to be compromised now.

"Maxie: I don't understand... how could water be good?"
 * The Ruby arc of the original Nuzlocke Comics has Maxie releasing Groudon to "end all water"... and then dumbfounded when people start dying of heatstroke.


 * Exterminatus Now shows us Virus prepared to exorcise a daemon-possessed toaster. With holy water.
 * Vexxarr has this gem of AI problem solving (they are trying to make a self-propelled explosive bait): take a small missile, glue your bait over it, tell it to compensate for extra mass in wrong places. What's wrong? See the next page. Followed by the team realizing they have no idea as to how the next stage is supposed to work.

Web Original
"Gohan: I'm not going to back down. I might be younger than you, smaller than you, weaker than you, and much less experienced, but I learned more about peach farming than yo-I think this was a horrible decision. Recoome: Recoome agrees."
 * In The Salvation War, after the demonic general Abigor hears of the defeat of (most of) his cavalry attempting to charge a ridgeline with "cowardly mages throwing mage bolts, with mage-bars in the ground and silvery snakes in the ground that cut up demons and their steeds alike" (paraphrasing here), his plan for the second day of fighting is to extend his lines by thinning them—by the time he was done, an almost-fifteen-mile-long front! -- so as to outflank and envelope the enemy, while ordering massed use of demonic bolt "fire" to suppress the mages. Too bad he didn't realize that he would only be able see a small portion of the battle at any one time, and thus would have to keep riding back and forth along the lines, until he was already on the front lines in the midst of the carnage, with multiple rockets headed his way....
 * Kevin Murphy puts the exact phrase into the mouth of the Scott Ian-looking Geat who makes a spectacularly failed attempt to charge Grendel in the 2007 Beowulf Rifftrax.
 * In Dragon Ball Abridged Gohan suddenly realized mid sentence that his decision to challenge Recoome to a fight after Recoome had already wiped the floor with Vegeta, a much more powerful fighter, was a bad idea.


 * Early in Yu-Gi-Oh the Abridged Series, Mokuba laments his poor foresight upon realising that using a Bedsheet Ladder generally only works if the sheet is long enough to reach the ground floor. Fortunately for him, he's a cartoon.
 * The Spoony One puts this in the mouth of the main villain of Highlander the Source when he gets the Quickening at the top of a tall tower.
 * The plan that Leeroy's raid group comes up with for taking on the Rookery in the Leeroy Jenkins Video ignores two key facts:
 * 1) Scattering the whelps of the Rookery only keeps them off you for a few seconds and will likely bring more to bear on you—you really want to hatch as few of them as possible. Fear rotation is rather pointless in the Rookery anyway due to the rate at which the eggs respawn.
 * 2) The paladin ability Divine Intervention does not allow a protected character to use any skills and is very much wasted on mages (who primarily rely on skills such as AOE attacks) and has the added "bonus" of killing the paladin who uses it, removing a character with the ability to tank and heal from the general fight.
 * Half of what Jay does. For example, breaking into Alex's home. He drops his flashlight, and then runs into the Operator.

Western Animation
"Haylee: Mom stole my boyfriend! Stan: Your boyfriend stole my wife! Let's get back at them by dating each other! Wait a minute. Daddy didn't think that through."
 * In one episode of Justice League, Copperhead attempts to gain leverage for an escape by jumping onto Hawkgirl's back, positioning his poison fangs near her neck, and ordering her to fly him out. She flies up a few hundred feet and stops. When Copperhead demands to know why, she notes that his threat is no longer as effective, since if he bites her neck she'll fall to the ground and they'll both die. "Didn't think this through, did you?" After she touches down, Green Lantern congratulates her on the bluff; her reply is a deadpan "Who's bluffing?"
 * In another episode, Downpour, a pastiche of one of the Wonder Twins, tries to kill Aquaman by hitting him with a torrent of water. Aquaman just stands there with a raised eyebrow: "'King of the Seas', remember?"
 * Downpour's follow up wasn't particularly well thought out, either. He rushes up to Aquaman and punches him. Ineffectually. Aquaman responds with a backhand slap that takes Downpour out instantly. In fairness to Downpour, he's supposed to be brain-damaged and visibly losing his mind in this scene - Copperhead, on the other hand, has no excuse.
 * Invader Zim:
 * Zim has this as a personality trait; as The Other Wiki once described him, "Zim has a crafty sort of intelligence, but he tends to think precisely one step ahead of his current problem". For instance, Zim builds a stasis-field device in one episode which subsequently explodes, but the fireball is slowed by the stasis field until it's expanding at less than walking pace. However, it will eventually grow to the point where it'll consume Zim's base along with the entire city. Zim's brilliant plan to stop this? Simple. He'll just cancel the stasis field. Despite being warned by his computer, and even his Cloudcuckoolander sidekick, that this is a really, really bad idea, he goes ahead with it. Hilarity Ensues.
 * The Tallest also seem to suffer from this, resulting in conquered planets being turned into massive parking lots because they didn't know what they'd do with the planet after conquering. They also ordered enslaved races to build weapons for them, resulting in the Megadoomer needing a massive extension cord and cloaking everything but the pilot and said extension cord.
 * Family Guy: In the episode "Blind Ambition", there is clip of one of Peter's (or both his) Siamese twin ancestors each fighting opposite sides in the Civil War. The one who fought for the Union killed the other, who continued decomposing until he was a skeleton. "Nope... Did not think that one through," he said to a bartender who asked about the skeleton.
 * American Dad: The episode where Francine gets poorly-aimed Laser-Guided Amnesia, she runs off to Burning Man with Haylee's boyfriend. This exchange happens when Stan meets up with Haylee at Burning Man:

"Zuko: I thought you thought this through. Sokka: I thought you told me it's okay not to think everything through! Zuko: Maybe not everything, but this is kind of important."
 * SpongeBob SquarePants: For a protozoan who goes to college and makes highly elaborate plots to get the Krabby Patty formula, Plankton can be a little slow when it comes to thinking ahead of his goals. For example, a robot made to look like a customer enters the Krusty Krab. Eugene Krabs, smelling an obvious trap, takes the place of the register. To his astonishment, the robot just asks for coral bits and even pays him money after its given its order. Suddenly, Plankton, who somehow managed to hide INSIDE the dollar bill (even for someone his size, there must have been some Hammerspace in there), pops out and gloatingly order Krabs to hand him the secret formula. Krab's response: "Or What?" Plankton: "I don't know. I never thought I'd get this far." Krabs: "Well then, allow me to suggest your next move" (flushes him down the toilet).
 * The Jimmy Two-Shoes episode "The Big Drip" has Lucius destroying every washroom in Miseryville to torment Jimmy during a Potty Emergency...including his own.
 * And pretty much any plan Jimmy and Beezy devise (alone or together) without outside input.
 * Avatar: The Last Airbender: Zuko, such as when he kidnaps Aang in the North Pole in the first season finale or when he tried to steal Appa from Lake Laogai. He gets better, eventually.
 * Zuko's so bad with it that it's contagious.

"Homer: I've figured out an alternative to giving up my beer. Basically, we become a family of traveling acrobats! Marge: ... I don't think you thought this through."
 * The Bugs Bunny cartoon Jack Wabbit And The Beanstalk has Bugs challenging the giant to a duel. "Take twenty paces, toin, and fire. Got that, shorty?" As the giant takes his paces, he disappears into the horizon and Bugs thinks he's outsmarted the giant. But then the giant reappears over the other horizon—the twenty paces were enough to circumnavigate all the way back.
 * From the "Dog Of Death" episode of The Simpsons

"Jake: Nah... That could never happen. Finn: You didn't think this through enough. IT COULD HAPPEN!"
 * From the "Her Parents" episode of Adventure Time


 * Turned into a Running Gag with Mojo Jojo in The Powerpuff Girls. To the point where when a spree of robberies occurred in Townsville, the girls automatically ruled out Mojo because it was too well thought out.
 * Wacky Races - Every single time Dick Dastardly Stops to Cheat. It's never enough that he is ALWAYS miles ahead of every other racer, he not only has to stop to lay a trap, but also stays behind to see the payoff, which ALWAYS puts him in last place. The most absurd example was the episode where he got stuck in the mud, and pulled out by a farmer with a donkey. He decides to buy the donkey, thinking that the farmer will no longer be able to pull the other racers out. Never mind that 1) almost half the racers have some gimmick that allows them to get out on their own, including a dragon that can dry it up completely, 2) the farmer OBVIOUSLY has several beasts of burden besides the one he sold and 3) Just what the heck will he do with a frickin' donkey?!
 * In Avengers Earths Mightiest Heroes Absorbing Man occasionally absorbs things he really shouldn't. When fighting the Hulk as metal, he absorbs rock. The Hulk promptly breaks his arms off. The metal form might not have let him win, but was at least keeping him in one piece. Much later he absorbs Mjolnir, and Thor reveals that he can now control Absorbing Man just like he does Mjolnir, and starts hitting people with him.
 * In an episode of Rugrats the babies imagine shrinking down and traveling into Chuckie's stomach to take out a watermelon seed he accidentally swallowed. Angelica however reveals her intention to actually water the seed so it grows and causes Chuckie to explode. She succeeds and gloats evilly, until Tommy points out it's going to explode with her inside it.
 * In the ThunderCats (2011) episode "The Forest of Magi Oar," the young hero Lion-O begins to recognize and Lampshade Hanging his own lack of forethought. When he uses his gauntlet's Grappling Hook Pistol to latch onto a retreating Giant Flyer Viragor, Lion-O has just enough time to realize "maybe this is a bad idea" before he gets violently dragged along for the ride. Shortly thereafter, he faces down the charging Big Badass Bird of Prey after tossing his weapons aside. Again, he muses, "probably another bad idea," seconds before it grabs him in its talons. The latter gamble does manage to pay off, since, on a hunch.

Real Life

 * Most people make this mistake in everyday situations when they know the results of a missed variable can be ignored or worked around (e.g. if you reach for a tool that you forgot to prepare, just get up and retrieve it). Bad things tend to happen only when too many of such mistakes line up and cause a chain reaction.
 * Water ruins the radar-absorbent coating of the F-22 Raptor. You can fly it in the rain all you like, it just won't be a stealth fighter afterward. The designers were aware of this flaw, it's a result of an inherent limitation in the materials, not a lack of foresight.
 * In fact, many military projects fall into this, as it often appears that the designers seem to have a tendency to be so enamored with their new project that they forget to take various practical issues into consideration. Of course, that doesn't mean that the projects aren't worthwhile, with the benefits outweighing the problems. Also many of the ones that don't seem to have been thought through are in fact stepping stones towards more reliable applications of the technology.
 * The F-22 for example was a development on the earlier stealth aircraft, the F-117 and B-2. The B-2 needed vast climate controlled hangers to keep its stealth working, while the F-117 necessitated it traveling relatively slowly (sub-sonic) to maintain stealth. The F-22 also needs climate controlled hangers, but much smaller ones than the B-2 and it can fly twice as fast as the F-117 while being even harder to detect. The F-22 is certainly a high maintenance aircraft, but is also the most stealthy (lowest radar cross section) of all manned aircraft, and will probably remain so for some time to come. The next stealth aircraft (the F-35) has in fact taken the stealth and speed down a notch in order to make the stealth technology more robust. The idea being that the F-35 will be able to have as little downtime as conventional attack aircraft while maintaining a good degree of stealth.
 * It is also worth noting that while the US government is happy to sell F-35's to other nations, the F-22 remains a state secret. To give you an idea of why... When the F-117's flew over Iraq in 2003 they were ridiculously good at penetrating air defenses (They made up 3% of the aircraft and hit 30% of the targets in the first 24 hours) and what with the F-22 having about 250 times smaller radar cross section and can fly faster... Yeah. She needs a lot of love, but she's way too good to trust anyone else with.
 * In war games, lone F-22s have single-handedly destroyed entire squadrons of F-15s. Yeah, no mystery why they keep them around even with the water vulnerability.
 * Which isn't even that much of a vulnerability; even a degraded stealth function is still enough to make it enormously difficult to get a lock-on, which is all the F-22 needs in its role as an air superiority fighter. Its role as a ground-attack aircraft requires it to sneak past enemy radar networks with total invisibility... but fast-mover ground-attack missions aren't scheduled during rain anyway because you need to be able to see the ground.
 * A rather better military example would be Project Pluto, the supersonic low-altitude nuclear-powered nuclear ramjet missile developed by the U.S. military (the fact that they seriously considered building that thing counts already). Project Pluto's real problem was that it was overtaken by ICBMs during its development. Aside from the difficulty in test firing it (which wasn't as crippling as it sounds, it might be an environmental disaster on wings, but this is during an age predating the green movement, meaning that a bit of isolated water in the Pacific would do), the project had a serious chance to turn out as a practical nuke 'em to hell option. Its just that ICBMs are more practical, being faster, cheaper and harder to intercept; they may not irradiate such vast swaths of enemy land by merely flying over them, but once the major cities are gone, that hardly matters anyway.
 * Australia's problem with the Cane toad. Because of Cane beetles destroying sugar cane crops, a bunch of Cane toads were imported to get rid of them. Only problem was that the toads couldn't even jump that high, so they ended up being unable to eat the beetles that were on the tall stalks... which caused them to eat everything else. And then they started infesting and taking over... combined with how they're highly poisonous and can poison any animal that eats them. Yeah, that solution was not exactly the best thought out.
 * It doesn't help that cane beetles and cane toads aren't active at the same time of day, so they don't ever even interact.
 * Another Australian one: The Murray River was destroyed in an attempt to bring over European farming techniques without realising that Australian soil was ill-suited to the endeavour. Clearing of trees for land led to salt buildup, which poisoned the water and ended up clogging the river.
 * And yet another: Despite already knowing that Australia is the driest continent in the world (seriously, check out the sheer amount of desert there is), no government there had a sufficient water-saving plan aside from the restrictions. This came back to bite them in the arse when the country was engulfed in an extreme drought, the likes of which had not been seen for the past several centuries. Of course, now they have the exact opposite problem...
 * The Lake Peigneur disaster was caused by someone drilling for oil through a lake into a salt mine. Admittedly, they knew not to drill through the salt mine and just messed up when they were figuring out where to drill, but still.
 * A lot of video games have been banned for controversy, but few will actually get you arrested for owning, and The Guy Game is this due to lack of foresight by the developers. Here's how it was made: the developers, Topheavy Studios (obviously a proxy) went to the South Padre Isle Spring Break Festival, and pretending to be a TV game show, interviewed a bunch of buxom, fun-loving - and possibly drunk - young women, asking trivia questions; if said girl got it wrong, she'd have to take her top off. They figured this could use this footage to produce an M-rated version of You Don't Know Jack and market it to horny male teenagers. Problem was, they never bothered to ask the age of the "contestants", and one was under 18, making the game technically child porn. The game was recalled, and a lawsuit later put Topheavy Studios out of business. Ironically, IGN reviewed it, and based on gameplay alone, gave it a 7.5 rating, describing it as "solid, simple, and fun", if lacking in replay value.
 * During WW 2, the Russians strapped explosives to dogs trained to run at tanks. Once the tank ran over the dog, the pressure-activated explosives would total the tank. The only problem? They trained the dogs using Russian tanks made to look like German ones. But Russian tanks used diesel engines; German tank engines used petrol. When in doubt, they went with what smelled familiar. Hoist by their own petard indeed.
 * The Dog Bites Back. Though this is RUSSIA in WW 2, the only reason they weren't using human suicide bombers was because dogs are quicker and smaller.
 * A salesman showing reverse searching (which was a search for what people were searching the internet for) decided he would use "toys" as the keyword. Apparently, he didn't realize until too late what kind of toys people search the internet for from the privacy of their own homes...
 * Considering Rule 34, it would have been smarter to just skip the demonstration altogether.
 * Quaker Oats buying Snapple for $1.7 billion. Unlike every other drink in Quaker's line-up (including, for instance, Gatorade), Snapple has to be refrigerated. It was only after the deal had gone through that Quaker realized that it had a shipping fleet of exactly zero refrigerated vehicles. Refrigerated distribution outlets soon realized this as well, and colluded on a high price to deliver the Snapple. Eventually, Quaker would sell it for $300 million dollars to another company, long after Snapple's trendiness had faded.
 * Nazi Germany had a problem: with the US being officially neutral but unofficially supporting the Allied war effort, German u-boats could not be used to their full effectiveness in the Atlantic. Japan attacks the United States and war breaks out, and Hitler thinks this solves his problem as he can declare war on the US because Japan is an ally, and thus finally give his naval forces the freedom they need to effectively cut off Great Britain. Of course, this also means the single largest economic and manufacturing power on the planet now doesn't have to pretend to play nice either.
 * Criminals. This tends to happen to them a lot. In example:
 * A few would-be ATM thieves in South Africa decide to use explosives to open up an ATM. Once the bomb goes off, the money would be theirs for the taking! But, somewhere in thinking how awesome it would be to blow up an ATM with a bomb, they forgot to make an important consideration. Namely; paper money tends to burn. Hilarity Ensues.
 * There have been several cases of people walking into a business, filling out a job application with their real name, address, etc., and then holding the place up at gunpoint. Of course, it doesn't take too long for the police to find them.
 * One example was a bank robber who decided to rob a bank, that was across from the FBI headquarters, ON PAY DAY. Oops.
 * Even better. He did his robbery during lunch hour.
 * It wasn't just the local FBI field office but the local Federal Building. And this was before Direct Deposit existed. Armed agents of pretty much every alphabet agency in existence were standing in that line waiting to deposit their paychecks.
 * Another robber went up to a bank with a stick-up note...written on the bottom of his pay slip, which had his name, address, postal code, and telephone number on it. Of course, he doesn't compare to the robber who held up the bank coming right from his work at a construction site...still wearing his hard hat, which had his name on it. Neither of them are quite as stupid as the criminals who decided to draw masks on their faces with black marker.
 * Every crook who has ever attempted to rob a gun store.
 * Bonus points for the guy who tried robbing a gun store with a knife.
 * Official policy of communist states to deal with disaster? Issue a nationwide bulletin that absolutely nothing has happened, and everything is fine, and censor any attempt to bring it to the public's attention. Well the public still became aware of it, but by that time, it was too late to do anything about it.
 * Biggest example: The Chernobyl Disaster. It was one of many things that lead to The Great Politics Mess-Up.
 * The resultant policy of Glasnost the Soviet Union enacted after the disaster is another example, but in the reverse. Turns out, when you can't even feed your own people, enacting a policy of total transparency with the press is not such a good idea after all.
 * Operation Red Dog (or as the press called it, the Bayou of Pigs) was a plot by a small group of White Supremacists to invade and take over the newly-independent island nation of Dominica. The small nation had only been independent from Britain for two years, they didn't have an army and their police force was mostly inexperienced volunteers. The plan seemed sound at first: With backing from Canadian mobsters and - possibly - David Duke himself, they would storm the island with a small arsenal, and then seize the armory and police station. Then they'd initiate the most important part of their plan, reinstating Dominica's exiled former ruler Patrick John, and in return for doing so, would open and fund a casino on the island, along with a cocaine smuggling operation. Of course, John planned to kill the would-be insurrectionists had it worked, which it did not; they ran into a problem such folks never do in movies, not considering the loyalty (or lack of it) of the boat captain they hired. When said captain realized his clients were Klansmen and Neo-Nazis (evidenced by the Nazi flags and Confederate flags among the cargo, along with enough illegal weapons for a gang war) he called the FBI and the would-be insurrections were arrested before they even got started.
 * The Mongol Invasion of Japan. Kublai Khan was in such a rush that he ordered the Chinese boat builders to make a huge fleet (a fleet second only to the invasion fleet that launched the Invasion of Normandy) within a single year. The Chinese laborers had to supplement the sea-worthy boats with river boats that had no keel, and thus were unworthy for sea travel. Bad enough when you are crossing an ocean, even worse when that ocean is prone to violent storms and typhoons. The now-famous kamikaze lead to the single greatest loss of life in a disaster at sea in recorded history, with many of the over 3,000 ships sinking with most of their crew.