Angels and Demons has a huge gaping hole that not a single character sees. Great care is given to say how undetectable the antimatter containment is. The protagonists even go so far as to wipe out power to entire city blocks so that they can look for the containment device without any background noise. Yet no one thinks to look for the camera pointed at the containment device that is actively broadcasting. Since they are receiving video, there is a signal. Since there is a signal, it can be triangulated.
Left Behind is full of this, especially in the early books.
A nuclear assault on Israel ends in no casualties. You'd think that evangelists of every religion would be trying to link it to their own, there would likely be a large amount of conversions, and hard-core atheists would be trying to desperately come up with explanations as to how it could be a natural occurrence. Instead, everyone seems to just go about their business as if it hadn't happened.
Related to this, Russia launches a nuclear strike on Israel, despite Israel being known to have an essentially indestructible second strike capability with most of their missiles believed to be aimed at Russia. They also apparently think it's necessary to launch their ENTIRE arsenal of over a thousand nukes at Israel, leaving their nuclear deterrent completely depleted despite the fact that Israel is small enough to easily be annihilated by one or two large strategic nukes. This strike apparently triggers a response from neither Israel itself nor from any other country despite the fact that the Russians are clearly insane and no longer have any nuclear deterrent. Oh, and the reason the Russians launched this strike in the first place? Israel wouldn't give them the secret to their new miracle-gro formula!
Aha. Maybe the whole sequence of events was such a massive Big Lipped Alligator Moment for real life in-universe that there's an unspoken collective agreement to never, ever mention it again and try really, really hard to pretend it never happened! (Well, it makes as much sense as most of the rest of the franchise.)
Every child in the world disappears in the rapture, but some adults do too. All of these adults are "real true Christians." Somehow, this exceedingly obvious pattern is not noted.
Carpathia's Technobabble explanation for said disappearances is apparently accepted readily. Apparently all the scientists who would rebuke it for its inaccuracies forgot everything they knew.
Most of Carpathia's machinations require this to work. Asking countries to destroy most of their nuclear weapons and give the remainder to him? And they fall for it?
Honorable mention should also go to the Global Community Faith. Carpathia gets some religious leaders together, they hold a press conference announcing that as of now, all religions are now united into a new, only vaguely defined, faith. And everyone except newly converted premillennial dispensationalist Christians and the Jews are happy to go along with it.
Ironically, this is the most logically consistent conclusion we can come to, but it has one major flaw: the authors don't believe God predestines who is saved or condemned. The only explanation that can make sense of all the idiocy is contradicted by the authors themselves!
And then there's Carpathia's speech to the UN, which consists of a brief history of the UN, a list of the countries in the UN and the people representing them, and a few feel-good phrases that don't actually mean anything. All repeated in nine different languages. The fact that every person listening receives this as being the best speech they've ever heard implies that everybody on earth except Carpathia really is a massive idiot. (The book actually explains this as a form of mind control; anyone but Carpathia giving the speech probably wouldn't have been laughed off the stage, but only because diplomats have a lot of practice in being polite.)
Isn't Carpathia supposed to be the Antichrist? Maybe projecting a Stupidity Field is actually one of his powers.
Mentioned in one of Isaac Asimov's Black Widowers stories: One character mentions he's having trouble writing his story without it turning into an Idiot Plot, and was trying to find a way to prevent characters from asking the obvious question that would resolve the mystery. Their guest then causes another Idiot Plot in much the same way.
It is so full of potentially lethal errors in judgement by both the protagonists and antagonists that a strong argument could be made for the series consisting almost exclusively of Idiot Plot, particularly in the latter books.
The greater majority of the protagonists problems are caused by their own lapses in judgement and failure to communicate, to the point that it would take hours to list them all. They refuse to work together, they run off by themselves in secret (repeatedly), they almost never ask for help, and even those that *should* trust one another withhold secrets for no good reason. Not only does it allow the antagonists to win many of their conflicts, it also prevents the heroes from gaining the strength they need to oppose the Dark One. Fortunately, the antagonists also have this failing.
The White Tower rebellion plotline has turned into this. One side of the conflict has rediscovered several lost spells, has a large army led by a famous general, and has surrounded the White Tower, preventing most movement. The other side, inside the tower, are at each other's throats, constantly in-fighting, and are vastly outnumbered due to their leader being Too Dumb to Live. Not to mention the fact that the Chosen One will never make a treaty with the Tower because their leader ordered his kidnapping, and beating. Granted, the Black Ajah is doing its best to foster these problems, but one would think that the Tower's ruling body would, at some point, notice that they are in a ridiculously weak position, their leader is a fool, and remove her from power. And all this is going on with the final battle over the fate of the world just around the corner...
The whole thing ends with the White Tower raising Egwene and only because Elaida was captured by the Seanchan followed by Egwene calling the entire tower Aes Sedai disgraces because only Sylviana had the balls to do what was right.
If Bella were smart enough to stay away from Edward, there would be no series, period. For the first book specifically, almost every plot point is introduced because Bella does something idiotic. About the only plot point not directly caused by Bella is Tyler's death van, which was just a flimsy excuse to get the story running.
Bella's decision to wander Port Angeles alone, as it got dark, and in the back alleys, is how The Reveal is set up. A particularly gifted level of stupidity was required for her to do so, since Port Angeles (not a large city) is notably deficient in back alleys. Roving gangs of rapists are also uncommon.
Bella's decision to lead an innocent boy along to gain information is how the Love Triangle is set up.
Bella's decision to go to a meadow, alone, with an admitted Serial Killer, and let him wander around behind her, is how the great romance is begun.
In fact, it's even worse than that, as Edward warns her that if things were to go wrong and he were to lose control of himself and eat her, all of the suspicion would be on him and his family because he had been hanging out with her recently. Bella then proceeds to go out of her way to make sure no one knows about it, literally in an active attempt to help her potential murderer get away with it. Even Edward calls her out on how retarded this is.
Bella's decision to do as James said - regardless of the likelihood of him actually having her mother or the fact there were two more-than-capable vampires with her who could have at least given some advice - is what causes the climax.
The whole plot point of James having her mother could have been solved easily if Bella had called her mother and ask how she was.
The James plot could have actually been resolved even easier if the Cullens had just fought him earlier. The odds were seven-against-three in their favor. Oh, what's that? James' ally Laurent wasn't willing to fight for him? Okay, seven-against-two. Laurent goes on about how the Cullens are sure to lose because James is such an amazing fighter, but in the end, it only takes Jasper and Emmett to kill him anyway—if the whole Cullen family had attacked him and Victoria in Forks, they could have easily won without Bella nearly getting herself killed beforehand.
Keep in mind that if the Cullens had done this, Victoria wouldn't have carried out her revenge scheme, which spanned the next two books. Meaning that not only would the Idiot Plot climax of Twilight have been averted, so would most of the Idiot Plot conflict of New Moon and all of Eclipse. Well done, Cullens!
In the film version of Twilight, Bella feels insulted when Edward doesn't talk to her, so she spends weeks (possibly even a month or more) waiting to tell him off for being a jerk. As pointed out by RiffTrax, any normal person would've moved on after a few days or so.
The Cullens going to school in the first place. They don't enjoy it, they don't socialize, they don't need any more formal education, and they are dangerous bloodsucking monsters (one of whom is new to the "vegetarian" lifestyle and thus constantly must struggle to keep from murdering his classmates). So, what exactly are they doing there, other than going there for cover (how about homeschooling)? Even with that excuse, they still stick out like sore thumbs among the humans, so that it would actually be safer to "cover up" by just not showing themselves in public. Especially since they are at risk of sparkling should the clouds break overhead during the school day.
In New Moon:
Bella's decision to go cliff-diving without any prior experience, anyone else to help her out or save her, and any knowledge of how deep the water she's jumping into is, is how the climax of the story is set up to bring Edward home.
Arguably most of the second and third act of New Moon fits this. Edward has spent all of Twilight and the beginning of this book talking about how he loves Bella more than anything in the world, but is constantly terrified of something bad happening to her. She is then nearly killed by Jasper at the party (which Edward himself and Alice forced her to attend). Then Edward tries to tell her that he doesn't love her anymore (in order to keep her safe) before leaving. Bella spends the rest of the book completely believing this, without ever once considering that he lied to her or attempting to talk to him about it. Even when she knows that he curled up in a ball and didn't do anything while they were apart, even when she knows that he left to commit suicide when she supposedly died, even when he hugs and kisses her and clings to her when she shows up alive, and even when he returns to America with her, she still is either convinced that he's putting on an act for her or doing it out of guilt - or that she's dreaming.
Despite living in the present and having enough money to have every form of technology ever, Edward immediately takes Jacob's word for it that Bella has died, rather than check his email/phone for any messages about it, check Forks' newspapers for Bella's obituary, call anyone else to confirm what he heard, etc.
Not to mention—Jacob never SAYS that Bella died. He says that "[Charlie Swan's] not here. He's at the funeral." Which he is. He's at Harry Clearwater's. Edward is the one who jumps to the conclusion that Alice's vision of Bella's death has to be accurate... even though most funerals do not take place on the day of the person's death, and he knows better than anyone how fallible Alice's visions are. Edward doesn't even call back and ask Jacob whose funeral Chief Swan is attending. Later he even tries to lampshade this, saying that when he heard Charlie was at a funeral, who else's funeral could it have been? Evidently Edward thinks Charlie doesn't have anyone he's close enough with to attend their funeral besides his immature, selfish, abusive daughter.
Which is even worse when you consider that Alice was the one who had the vision and he had Alice's cell phone number! There was no reason he couldn't have called Alice directly! Alice herself doesn't help though, as she apparently thought it was a grand idea to hang around with Bella for a few days, instead of calling Rosalie and Edward and telling them "Never mind, Bella's alive after all."
Not to mention the fact that Bella, upon realizing Edward had left the country, went into a deep depression that had her bedridden for months. Her father, for some bizarre reason, didn't even bother to do anything (e.g send her to a psychiatrist) even though she was having severe night terrors and wouldn't leave her bedroom for months.
Or rather, he didn't try very hard. He brought it up to her once or twice that she might want to consider seeking professional help, but backed down when she demurred. Charlie's quite the milquetoast for a sheriff.
Not only is Bella an idiot, she's actually a human Idiot Ball! Anyone who comes into contact with her (most notably Edward) starts making random, ridiculous decisions and being generally Too Dumb to Live (the attempted in-universe justification that Bella is just so unique that she naturally provokes such reactions doesn't help). Even the villains suffer from this. Lets face it, how many of their thoroughly inept "wicked schemes" would have came close to working if the good guys hadn't been a group of shambling, dunderheaded simpletons?
The Cullens know that there's at least one newborn tearing up Seattle and they know that Victoria has been trying to kill Bella since the previous book. They then learn that there is a newborn army being built in Seattle and that a vampire has apparently broken into Bella's room and stolen one of her shirts. Common sense would dictate that Victoria had the newborn army made and ordered the theft of Bella's shirt so that the army could track her down and kill her. It's not until a good number of chapters later that they figure out that Victoria was behind the theft of the shirt and it's not until the actual climax that they realize that Victoria was behind the army of newborns.
This is particularly stupid given that Edward can read minds and Jasper can influence emotions. Logically, Edward could have gone to Seattle, read the minds of at least some of the newborns and/or their victims and determined who was behind this army, while Jasper projected calmness on the newborns that Edward discovered. The army members would have been identified, their secrets uncovered and their attacks rendered useless with comparative ease—and no one ever considers this. Not even Jasper, who is canonically the strategist.
It's particularly stupid because vampires in these books are supposed to have a natural tendency toward revenge. Yet none of the seven vampires in the Cullen group seem to know about that. Even forgiving that ignorance on account of their semi-pacifistic lifestyle, the wise, powerful Cullens still look to be horribly prone to narrow-minded thinking and underestimating their opposition. They seem unable to conceive that Victoria could be capable of a plan more sophisticated than trying to slip past Bella's two groups of supernatural bodyguards and kill our heroine before they can stop her. It also takes most of the book to occur to them that the newborns in Seattle could be Victoria's creations in order to bolster her forces with the Cullens protecting Bella again, even though Jasper once did the exact same thing.
The entire conflict of Bella and Edward being sexually frustrated but fearful of Bella being hurt could have been solved with a little more creativity on what sexual positions or activities they did.
Most of Bella's pregnancy throughout Part II could have been avoided entirely, given that the baby was developmentally at a point where it could survive outside of the mother. All Carlisle had to do was perform a caesarian and the baby would be slightly premature. The kicker is that they were planning on doing just that... but wanted to wait until it was pretty much the nine month development and leave Bella in agony, for some unfathomable reason.
During Bella's pregnancy, Carlisle is flummoxed about why the fetus is slowly killing Bella, and even exclaims, "I can't figure out what it wants!" Even though they've never heard of vampires being capable of sexual reproduction, they still know who and what this thing's parents are and where the inhuman aspects come from...
The Short Second Life of Bree Tanner only gels with the plot of Eclipse because the characters have all been severely lobotomized. Despite the fact that Bree knows that Riley is kidnapping teenagers to become vampires, that he makes no effort to protect them once they've become vampires, and that he kidnapped her himself (breaking her arm and severely terrifying her in the process), it's not until the very last few pages that she actually gets it in her head that he's a bad guy. This results in her death at the hands of the Volturi after she fails to make any attempts to escape before the final battle (including one instance where another character directly offers her a foolproof chance of escape) despite knowing the sun can't hurt her and Riley not being able to reveal otherwise without losing control of his army, all because she can't see past Riley's paper-thin lies about Diego - who she's totally in love with despite having only known him a few days, by the way - most certainly not being dead.
This novella also retroactively makes Breaking Dawn into (even more of) this trope, because Bree mentally gives Edward her knowledge of the events leading up to the battle, which includes how the Volturi were willing to turn a blind eye to Victoria's plans, in the hope of the Cullens being killed. This means that Edward at least was well aware that the Volturi were actively trying to get his family killed... but in Breaking Dawn, he was quite shocked at the idea of the group being so corrupt.
The title character would have never sunk his fangs in Mina's neck if the heroes had remembered anything they'd learned about vampires during their ordeal with Lucy. Especially since Mina was displaying all the symptoms of being a vampire victim that Lucy displayed earlier... Exacerbated by the fact that Mina was with her when Lucy was first attacked and started displaying those symptoms. And they had Van Helsing with them the whole time.
The way Lucy's mom undermines every effort to save her. Really looks like she's doing it on purpose.
Also for an all powerful vampire, you'd think Dracula would have had more common sense. Such as taking Lucy with him after fully vamping her rather than leaving her behind. Not only did he give the heroes an example of what a vampire was like and what they could do - he practically led the heroes straight to him. What's the point of making undead women if you're not going to use 'em?
Another vampire example, the entire plot of Barb Hendee's Hunting Memories depends on the heroine's (using that term loosely, since she is a mass murderess) stubborn refusal to even consider the possibility that the villain (arguably, he is just defending himself) has completely given up after the end of the first novel, and will never try again, even though he was clearly a fanatic. One of her companions, who knew the villain much better, didn't think he'd just give up.
There's this empire in Africa which conquers everything it can grab (talking about whole continents here), enslaves pretty much everyone, has an extremely supremacist ideology, plus supreme technology, acts like it's independent even while being a British colony, but no one - whether Nazis, Communists or good democrats - decides to do anything to stop them.
The premise is that the Draka are a sort of Evil Twin society to the United States. Historically, no major nation decided to stop the US from becoming powerful from 1812 up to World War II. The catch, and this is where the idiocy comes in, is that the US wasn't deliberately expanding into the spheres of interest of countries powerful enough to stop it, except for a few minor border clashes with the British Empire over a river valley here and there. Whereas the Draka do, especially during their alternate version of World War One.
There's more idiocy to that, because during much of their power grab the Draka are still a British Dominion, and not once does the British Empire even attempt to slap them down despite repeated brutal, hostile and illegal actions.
There's an attempt at justifying it in the story, arguing that the British Empire was so traumatized by the loss of Canada in the War of 1812 that it didn't feel powerful enough to impose its will on the colonies. (In Real Life, the British Empire at the height of its power barely won a war against two insignificant republics in a small part of what's now South Africa - it's an open question how it would have fared against a heavily militarized, technologically advanced power controlling a large part of a continent.) The Draka are also very careful not to tread on Britain's toes until they are powerful enough to get away with it.
Completely left unaddressed is the presence of France in the presumptive Drakan empire. The French presence in west Africa was well-established by the time the Draka get there, and France is almost as powerful as Britain during the 19th century (they have the second-largest navy in the world, and the largest modern army, during this period). Why there wasn't a more generalized conflict between Britain and France over a rogue British colony impinging upon the French sphere of influence (or why the French didn't just send the Draka home with their asses firmly kicked) is an exercise for the reader.
This site does a good job of pointing out most (though not all) of the flaws in logic, not to mention the blatantly illegal things done by the Draka while they are still firmly under British rule (illegal under 19th century British rule that is).
Pretty much everything that P. G. Wodehouse ever wrote, but the man was so incredibly good at it, you barely notice. Plus, let's face it; when you're dealing with characters like Bertie Wooster, what else do you expect?
Being There, both novel and film, is a satire that uses an Idiot Plot to help make its point. The whole story hinges on how people who believe themselves to be sensible and intelligent nevertheless jump to their own, desired conclusions time after time in their dealings with Chance the Gardener, never asking the questions most people would be tempted to ask based on what he says. This is partially because he appears to be a sensible, intelligent person himself, but is in fact an imbecile who doesn't understand what's going on and thus isn't able to correct others.
The entire Dutch novel Descartes' Dochter (Descartes' Daughter), which revolves around the discovery of a lost manuscript of Descartes. When the main character Henriette returns home to her girlfriend Maartje in a coat covered in blood, Maartje gives up trying to find out what happened after a half-assed attempt at questioning, and the two proceed to make love. Later in the story, when Henriette murders her own mother, Maartje does not go to the police, does not get the hell away from Henriette, but e-mails the French professor she has been corresponding with about it. Who responds with only some vague philosophical stuff about "the gift". Later on, Maartje converses with a German professor about a lost manuscript of Kant that has turned up. When the German professor hears that Maartje has also been corresponding about it with that French guy (the actual French philosopher Jean Luc Marion), she exclaims: "Oh no! A Catholic!" and takes a train to Holland straight away, where she is immediately murdered by Henriette. Later, Henriette lures Maartje into the toilet on a train and then kills her. Serves her right for being Too Dumb to Live.
They accidentally drink the Love Potion meant for Isolde and Mark. They don't even consider asking king Mark permission to marry or anything. Granted, an oath is a pretty big thing, but so is permanent magic, and it's not like Mark cared that much.
Kathy Reichs' Temperance "Bones" Brennan novels depend strongly on this trope for about half the plot, and nearly every major climax. This is particularly true when the climax involves the main character, who seems to pick up the Idiot Ball on nearly every possible occasion. Particularly when it would get her into yet another life-threatening situation by going somewhere alone and unarmed, no matter how many people are telling her not to, which she does in the majority of the novels. When other characters do this, it's either because they've picked up her Idiot Ball, or because they're Too Obsessed/Absent-Minded/Naive/Fluff-headed To Live.
Digital Fortress is a particularly bad example. Even if you ignore the fact that the plot relies on every single person in the world not knowing the very basics of cryptography, it still doesn't make much sense.
"Dismissed with Prejudice" by J. A. Jance. Let's see, the back cover tells us about a Japanese businessman found dead of an apparent suicide. But an error in the ancient ritual pointed to... murder! The actual problem, according to a Japanese-American investigator, is that the scene is "totally wrong" for the ritual suicide. But we have a Caucasian medical examiner persist with his theory of suicide. A couple days later, we discovered that the victim was indeed murdered — bludgeoned over the head. "We couldn't see it until after we moved the body."
House Rules is often criticized for this. Many reviewers note that the entire premise of House Rules depends on barely anyone asking Jacob whether he committed the murder or not. His mother and lawyer immediately organise an insanity defence instead. This is particularly glaring because one of the traits of Jacob's Asperger's is that he's terrible at lying. The plot would also be over in fifty pages if Theo didn't sit through his brother's arrest, jail time and trial, and all the strain this causes on his family, without telling anyone that he broke into Jess's house on the day of the "murder" and saw her fall down and hit her head. All right, maybe he's frightened of being charged with causing her accidental death, but when he finally owns up that doesn't seem to have occurred to him.
Classic of Russian SF Ivan Efremov'sAndromeda Nebula is a perfect example of Idiot Plot. Starship crew was trapped on the planet of Iron Star because watchkeepers just didn't want to wake their commander (despite they knew that he wanted to drive the ship in this area himself). On the planet they've found another Earthian starship, abandoned because it's crew was terminated by local agressive fauna. The last member of dying crew left a record, which contained nothing helpful - except the advice not to leave the ship, never (considering the fact that this record could be picked only by one who had already left his ship, advice is more than senseless). And it is just the beginning...
Blacklisted by Gena Showalter has a mild version of this. The Alien Investigation and Removal agency hunts down and arrests high schooler Camille and her crush Erik. First of all, why would she follow him, when he apparently seems to be a drug dealer? Even if you hand wave that to blind love, why would AIR not just ask her if she was with him or not? As seen in the companion book, their policy is to keep civilians out of their business. Instead they assume that she a drug dealer too and shoot and arrest her.
"The Deadly Mission of Phineas Snodgrass". So a man travels back in time and pretty much literally Gives Radio to the Romans. Okay, that's not the Idiot Plot. The society which this man creates develops the scientific method much more quickly than it arose in Real Life, and as a result is fully-modernized by around the sixth century and is practically Raygun Gothic by the Middle Ages. And the writer expects us to believe that in all that time no one in that scientifically-minded society ever noticed the massive overpopulation problem that was arising or took any steps to mitigate or prevent it? You'd think that, with no religious restrictions against such things, that reliable birth control would be invented as soon as their society advanced enough to discover modern medicine and learn what causes reproduction. It pretty much stretches Willing Suspension of Disbelief that the only way this advanced society could think to save themselves from an overpopulation-induced catastrophe was to send another person back in time to prevent their society from being founded. What are they, suicidal? Also, the Romans had a cultural lack of compunction about Offing the Offspring, as well as already understanding several modern birth control methods.
A debatable one in Dirty Little Secrets by C.J. Omololu. Lucy is the daughter of a compulsive hoarder who comes home one day to find her mother dead under a stack of junk. She starts to dial 911, but panics and doesn't dial. She was afraid that her friends might find out about how messy her house was and pity her. In the end, she burns the house down. She only calls her brother once, and gives up. Instead, she tries to clean up the house so it at least looks presentable. If she had just called 911 after cleaning up the house somewhat, she probably could have been better off. If she had even called her brother a second time, she probably could have avoided having to burn the house down.
Harry Potter and the Philosopher's Stone: you also have to question Dumbledore's wisdom in telling all the students at the start of the book not to try to get past a certain door. A certain door that can be unlocked with a simple charm and has an enormous, extremely dangerous multi-headed dog behind it, ready to maim anyone, adventurous student or not, who gets near. Not to mention the basic concept of putting something that you know the Big Bad is trying to get to in a school is just asking for trouble.
It is idiotic for Fake!Moody to have gone through all the trouble to turn the trophy into a Portkey and send Harry to Little Hangleton during the most conspicuous moment in the Hogwarts school year. A Portkey can be made to look like anything, so it would have made sense for Moody to have invited Harry to his office and made him touch a book or something there, with no witnesses. It's Handwaved as making people think Harry just died in the ridiculously dangerous tournament, but that would have been suspicious too since Harry was not supposed to be participating in the first place. And on top of that, Hogwarts is not known for being safe. If they really wanted to make it look like an accident, a much simpler and efficient way would been to take his body and dump it in the Forbidden Forrest, where there are dozens of creatures that could've potentially killed him, or threw him to the Whomping Willow, or even made it look like a broom flying accident, and that would actually be less suspicious than putting him in the Tri-Wizard Tournament as the fourth competitor and then try to guide him to win the tournament.
For that matter, everyone thinks Harry volunteered to the tournament. In the same book that introduces the Veritaserum, a substance the prevent people from lying. Couldn't they just give him a dose of it in public and ask him if he did volunteer? Instant name-clearing!
Voldemort tries to kill Harry (with a Avada Kedavra, the same spell that backfired horribly the first time) in front of his followers, instead of just letting him bleed out or having Pettigrew strangle him to death, then present the corpse to the Death Eaters. Also, he leaves an easily usable Portkey around while giving Harry the wand to get it, instead of just making the portkey after Harry's death.
The whole plot of the book occurs because Dumbledore doesn't stop to think that if he already has a separate copy of the Prophecy that Voldemort doesn't even know exists, simply destroying the one in the Department of Mysteries note Which is entirely possible: the protections prevent unauthorized people from lifting one from the shelves, but stray shots from the battle destroy prophecy spheres left and right safeguards the information for all time. So he instead get it guarded (by one guy under an invisibility cloak, something that wouldn't even slow down Voldemort), instead of just smashing it and replacing it with a random crystal ball he picked up in the gift shop, or some sort of booby-trap.
Worse yet, Voldemort holds an even larger Idiot Ball since he could just walk in and take the thing. Bellatrix responds to this by saying it's ludicrous to think he'd come right into the middle of the Ministry... except that that's exactly what he does 15 minutes later after the prophecy is smashed. It's not like he couldn't have sneaked in either: both his Death Eaters and a bunch of teenagers manage to get in undetected, and they have nowhere near the stealth Voldemort is explained to have.
Harry Potter and the Half-Blood Prince: The minor side-plot that gives name to the sixth book rests entirely upon it. It's traditional in (muggle) British schools for teachers to keep their favorite moth-eaten, scrawled on textbooks in the book cupboard with the books normally passed out to the children who forget their books, resulting in plenty of amusing anecdotes about the fights kids get into to avoid being the one stuck with that torn copy despite the fact it's often the most useful book to end up with. Whether Wizarding schoolteachers do it or not, Rowling clearly played on this, right down to Ron and Harry fighting over who got stuck with it, and yet somehow they were both completely incapable of ever wondering if it belonged to either the current or past Potions Masters. Not even Hermione was capable of wondering what really should have been an obvious first suspicion for a British kid in a British school system to have. Of course, if they had jumped to the logical suspicion, the sixth book reveal would have happened at the start instead of the end - although that would not have changed the overall plot of the book in any significant way.
Galapagos doesn't just abuse this trope, but positively runs on it in its entirety. The book is basically nothing but the characters acting like utter morons and the author dropping a Contrived Coincidence in their way all the time.
With House of Leaves, the Navidsons could just move out. It's a house. A scary, scary house, but a mostly nonmovinghouse all the same. Johnny could, you know, stop reading The Navidson Record. Pelafina could... stay insane? Okay, so not everyone has a simple solution.
Pretty much any novel by Michael Crichton is a combination of this and Murphy's Law run amok. It's usually not so much that every character is an idiot as that the ones who aren't idiots don't find out what the ones who are idiots have done until it's too late for them to fix it.
Artemis Fowl: The entire berserker threat would never have occurred if they had simply shot the future Opal BEFORE they put her in the tube and she became all powerful.
Luke tells Leia that force-sensitive babies are very susceptible to being warped by the dark side (despite the fact that such a thing has never been mentioned before or since, meaning Luke had his facts way wrong). Princess Leia decides that the best thing to do protect her new children is therefore to put them on a secret planet that not even she knows about, for two years alone with her best friend, completely undefended should the Imperials somehow discover the location (which they inevitably do). This whole plot would have been avoided had Leia realized she was being a little too paranoid and conceded that the kids would be just fine on the well-defended Coruscant growing up with them.
The spirit of the Sith lord Exar Kun is on Yavin IV turning the students at the Jedi Academy to the dark side. When Luke first hears about these strange happenings, one of the students gets killed, and another student openly attacks him and tells him that he's not as good as his other teacher, Luke decides the best course of action is to investigate... some other day. This gives plenty of time for Exar Kun to warp Luke's most promising student into getting a weapon of mass destruction and waging a star-exploding war on the Imperial remnant.
With said corrupted student, Exar Kun manages to get him to channel the dark side and put Luke into a coma where his spirit is sort of a force ghost. Later, the Sith Lord decides he needs to destroy Luke's body so that he could never return (apparently he never thought of that when he had the student put Luke into a coma), so he tries all sorts of over the top plans like making one of the students sleepwalk and lift Luke up with the force so he could be defenestrated and fall to his death in the jungle. Or summon a bunch of dark sided beasts to tear apart his body. It'd be much easier for him if he just got a student to sleepwalk, pick up Luke's lightsaber conveniently placed right next to him, then stab him where he lies. Also despite these constant attacks, the students at the academy are content with letting R2-D2 guard Luke and just hoping that someone more competent comes in time to save the day.
Terpfen, a Mon Calamari, is forced to act against his will to sabotage the New Republic because the Empire implanted him with a mind control device. Among other things, he sabotages Admiral Ackbar's B-Wing so it crashes into a populated area (causing him to resign his post), helps poison Mon Mothma, and reveals that baby Anakin Solo is hidden on the planet Anoth. When he becomes free of the mind control in the third book, Terpfen could just walk down the hall and tell any of the New Republic leaders what he did so that they can reinstate Ackbar, start creating an antidote for Mon Mothma, and send a whole fleet to intercept the Empire en route to capturing Anakin. But that doesn't occur to him.
It gets worse. Instead, he decides to go down to the hangar, assault the ground crew and hijack a ship, dodge the pursuing fighters around space debris (unintentionally killing one), and hightail it to Yavin IV so he can personally warn Leia (who is visiting there), so she can go to Mon Calamari to recruit Admiral Ackbar, so they can send one lone battleship to Anoth to engage the Imperials capturing baby Anakin. After he is safe, Terpfen tries to kill himself out of guilt, but Ackbar decides to spare his life. Fortunate too because by the time they get back to Coruscant, Terpfen finally remembers that he helped poison Mon Mothma and tells them how to cure her. Again, this could have all been resolved much more quickly (not to mention prevented any risk of the Empire reestablishing their mind control link before he revealed his sabotage, Mon Mothma dying of her poison, the New Republic battleship being outgunned by an Imperial fleet of unknown size, or the Republic capturing Anakin and then leaving) if Terpfen had just walked down the hall on Coruscant and told the other New Republic leaders about what he'd done.
And what would have happened had Terpfen failed to hijack the ship? He would be taken into custody and asked why he did it, at which point he'd reveal the sabotage and things would be solved just as easily as if he'd told them in the first place!
Unless the guards just shot him (which they tried to do). Hence, idiot plot.
The Adventures of Archie Reynolds functions entirely because everyone is a moron. The plot involves three boys who discover a secret passageway, which eventually leads to stolen jewels and the rescue of a kidnap victim. However...
The door to the secret passage is out in the open where anyone could see it. That's how it's discovered.
The criminals left a clue leading to the combination to a safe right on the safe itself, assuming no-one would figure out the world's most obvious clue.
When the kids discover the jewels inside the safe and steal them, the criminals decide to recoup their loss by... kidnapping a random neighborhood girl, and keeping her hostage in the exact same area as their stolen jewels, which is how Archie discovers her.
Mary Shelley's Frankenstein. For all Victor's impressive scientific knowledge, he is an impulsive, self-centered idiot who never once plans ahead. He gets all wrapped up in creating the monster and makes no contingency plans at all for what might happen after he brings it to life. During Justine's murder trial, he just sits there looking stupid while his otherwise completely passive adopted sister acts as Justine's character witness, when he could prove her innocence easily (the time in a mental hospital that would probably result is peanuts compared to the life of an innocent). When the creature tells him to create a bride for him, Victor destroys the unfinished female rather than finish it out of fear that the two would reproduce (given the knowledge of human anatomy which we know he has, he could just "forget" to add a uterus and the problem's solved). Instead, his whole life gets destroyed and his loved ones are collateral damage.
The gamebook Search for the Nile. The protagonist, a contemporary kid, goes into the past; his quest? To find out what the source of Nile is. No, not to bear witness to its discovery, or anything like that; his mission is specifically to find out what the source of Nile is, and he treats it as a huge mystery he is desperate to unravel. Why couldn't the protagonist just look it up in an encyclopedia instead of going on a dangerous trip to untamed Africa is unexplained. Note that, in this series, the plot of each book is typically about unraveling some genuine historical mystery.
Pretty much all of Hunted. For starters, End of the World as We Know It has just begun, Raven Mockers potentially everywhere and anywhere waiting for them to venture above ground, the weather outside is blizzard conditions, so what does Zoey do? She goes outside with Heath to say goodbye. It just so happens that a Raven Mocker is outside (waiting for her specifically) and it then goes to attack Heath. Now Zoey could have done many things here. She could have summoned her elements to immediately and attacked the Raven Mocker, or dragged Heath to her and headed back to the Depot, or headed towards Heath's car and used it for cover while she thought of something to do or screamed for help (what with Erik being relatively close by). What she does do is push Heath out of the way and takes the hit for Heath instead and almost ends up nearly dying because of it. Um What? The idiocy is futher compounded due to the fact that Zoey has already fought off Raven Mockers before by using her elements.