The Comedy of Errors: One character has been searching for his long-lost twin, and comes to a town where said twin actually lives, causing him to be recognized by everyone and confused with his twin. Mistakes abound, and Hilarity Ensues. You'd Expect: That he'd come to the obvious conclusion that his search is over — his twin lives in this town, and the character's just being mistaken for him. Instead: He grows progressively more and more confused about everything that happens and ultimately concludes that the entire town's full of witches who are tricking him. Nobody figures it out until the twins come face-to-face.
In the 2007 version of Hairspray, Tracy wants to join the Negro Day Dancers to march against segregation in "The Corny Collins Show" in order for blacks to be allowed to dance on television. You'd Expect: Tracy would listen to her mother about why it won't be a good idea for her to join the march, since she can be jailed for doing so. Instead: Tracy joins the march, assaults a policeman with her sign, and nearly gets herself arrested.
Shakespeare is not immune to this. At the end of Act 3, Scene 3, Hamlet has just received confirmation that his uncle Claudius did, in fact, kill Hamlet's father. Claudius is in a confessional, alone, praying desperately to God for repentance and mercy. He does not see Hamlet enter, dagger unsheathed, seeing the time ripe to avenge his father's death. Minor hindrance: as a man in prayer, if killed at that instance, Claudius would go to heaven. However, Claudius' prayer is insincere; he cannot feel remorse for his brother's murder. You'd expect: Hamlet, like the son of a king, would alert Claudius out of his prayer and provoke him to a fight. When Claudius is enraged, swearing, and other damnable things, Hamlet skewers him. Since Hamlet would be King himself if he killed Claudius, it doesn't matter in the least what anyone else thinks, so why doesn't he do it? Instead: Hamlet reasons that killing Claudius and sending him to heaven is not fair for Claudius killing King Hamlet and sending him to hell. He sits there for a while explaining this out to himself, and then, a Momma's Boy to the very end, he decides he shouldn't keep Queen Gertrude waiting and goes out to meet her. This results directly in Polonius's death, Ophelia's suicide, and, well, you know the rest.
Love Never Dies: Meg Giry loves the Phantom, who loves Christine Daae even more. In the climax, she snaps and abducts The Phantom and Christine's son Gustave and threatens to drown him. The Phantom talks her out of harming the boy but must now talk her out of shooting herself. You'd expect: The Phantom would kindly talk her into handing him the gun. Since this is an emotionally-damaged young woman, the Phantom would do so by emphasizing with her feelings of abandonment and assure her everything'll be all right. Instead: The Phantom does so until he tells her "Beauty sometimes goes unseen/We can't all be like Christine.'' This sets Meg off once again and leads her to accidentally shoot and kill Christine.
Madame Butterfly: A young woman named Cio-cio-san aka Butterfly marries an American man named Pinkerton, against the opinion of pretty much everyone in their surroundings. It's also stated that Pinkerton married Butterfly just temporarily, and has no intention to actually stay by her side for more than a month. Pinkerton then leaves to the USA almost immediately after the marriage, and Butterfly is all alone for two/three years — while her maid Suzuki, the USA consul Sharpless and even the matchmaker who got her hitched to Pinkerton, Gorou, have told her to not wait anymore for him. You'd Expect: Butterfly to consider her difficult situation (she has a young child fathered by Pinkerton, her family save for Suzuki has disowned her for converting to Christianity, they barely have money to scrap by, etc.) and decide that she cannot just stay there waiting endlessly. Even if she still loves Pinkerton, which is understandable since he's her First Love and Butterfly herself is merely in her late teens, it's best for Butterfly to be pragmatic and think of her own well-being — and specially, her kid's own well-being, as the boy is already being looked down on for "not having a father". Instead: She keeps waiting for Pinkerton, blindly believing that as soon as he returns, he will stand by her and everything will be okay. She also refuses all the warnings from Suzuki, the pleas from Sharpless, and Goro's offer to get her a new husband. Predictably, when Pinkerton does show up, he brings his new American wife Kate and intends to take their kid to the USA, leaving Butterfly alone in Japan. It goes as well as you expect.
This is also a big-ass opera of idiocy for Pinkerton. When he comments to Sharpless in the First Act that he doesn't really intend to stay married to Butterfly, Sharpless immediately tells him not to be an asshole and that Butterfly, despite being aware of how easy divorce is in Japan, considers herself as his full-blooded wife and will not relinquish that. You'd expect: For Pinkerton to at least be considerate enough to keep an eye on this girl who, according to Sharpless, completely trusts Pinkerton's good will and love. Even if he cannot take her to the USA or stay in Japan, you know, not being an ass to Butterfly is at least in minimal good taste. Sharpless is also a guy who seems to be very savvy about Japanese society (he is the American consul after all), so his word shouldn't be taken lightly. Instead: Not only Pinkerton doesn't give a crap about Butterfly's feelings and stays away for three years without apparently contacting her, but he does marry this American woman named Kate and brings her with him to Japan. As said above, Butterfly does NOT take it well.
Peer Gynt: Ingrid, the sole daughter of the Hægstad farm, has been sweet on Peer for obvious reasons. His mother knew this.
You`d expect: Mother Åse to vouch for Peer long ago (before the play really started), securing Peer the biggest farm in the area, and a secure economy for herself. You`d also expect that Peer would be smart enough to go for that solution.
Instead: Peer crashes the wedding of Ingrid and another guy, to be rejected by a newcomer girl, then hijacking Ingrid, and then making himself an outlaw, losing every property right to his father`s farm, and in the end also indirectly causing Ingrid`s farm to go to pieces. What an Idiot.
Then there is Solveig, poor girl. Peer meets her at the aforementioned wedding party, and he asks her to dance with him.
You`d expect: That she follows custom and at least tries to be nice to him by trying a round of dancing. After all, that was all he asked for.
Instead: She rejects his request because she has heard of him and his antics, and because she is rather prudent. From this rejection comes Peer`s fatal crush on her, his eloping with the bride, his meeting with the trolls, and the whole mess finally making him an outlaw. Solveig admittedly sought Peer out to set things straight, and thus she lived in his cottage the rest of her life. So, Solveig, denying Peer Gynt one single dance turned into a lot of problems for both of you.
The Phantom of the Opera has this with the new managers Andre and Firmin. When the curtain crashes in the beginning and scares away Carlotta, Mdme. Giry presents a note from "The Opera Ghost" that demands 20,000 Francs among other things. You'd expect: that the managers contact the police to find the Phantom, since they've only just taken over the opera house and aren't influenced by the actors' superstition. Instead: they ignore his demands, which leads to Christine being kidnapped (twice), two men being murdered, the chandelier being destroyed, and the company going out of business.
They do this again later in the show. When Christine is first kidnapped, the managers, Raoul, Carlotta, and Mdme. Giry receive notes from the Phantom listing various demands. The note from Giry has demands for everyone present, which boils down to "In your new production of Il Muto, you will therefore cast Carlotta as the page boy [mute part], and put Christine in the role of Countess. If you don't, bad things will happen." You'd expect: that Andre and Firmin would contact the police. If not, then they'd just cast Christine anyway, considering that her previous performance was very well-received with critics and the audience. Instead: they ignore his demands and cast Carlotta as the female lead, which leads to the Phantom being pissed. He drugs Carlotta's spray so that she loses her voice. Christine becomes the female lead anyway, Joseph Buquet dies by the Punjab lasso, and the chandelier crashes down to the stage, nearly killing more people and costing who knows how much to replace.
Earlier, when Christine wakes up in the Phantom's lair after a rather stressful night, she realises her 'Angel of Music' is in fact a mortal, masked man who happens to be absorbed in playing the organ. You'd expect: that she would either look desperately for a way out, since hey, she's been brought down here by said strange masked man for who knows what nefarious purposes, or ask him - from a safe distance - what the heck is going on. All while not so much as even thinking of touching the mask, since if a man keeps only half of his face covered, he's probably doing it for a very good reason. Instead: She sneaks over to him without revealing her presence, whips the mask off and reveals the deformity underneath - and then is surprised that the Phantom is furious with her.
When Raoul is being guided down to the Phantom's lair by Madame Giry during the climax, she keeps reminding him to hold his hand at the level of his eyes, so that the Phantom can't nab him with the Punjab lasso. When Raoul finally reaches the lair and demands to see Christine, the Phantom sarcastically says 'Be my guest, sir,' and raises the portcullis so Raoul can duck inside. You'd expect: that Raoul would be rightly suspicious at the Phantom suddenly being so obliging - especially since the first time they met face to face the guy tried to kill him with fire - and would be on his guard for any lethal tricks he might pull instead of just racing over to hug Christine. Instead: Raoul naturally fails to do what Madame Giry reminded him of several times, and consequently the Phantom is able to noose him and hold him hostage in order to force Christine to submit to his whim. Nice rescue there, Raoul.
The 2004 film version takes the idiocy even further: at one point the Phantom and Raoul have a sword fight in the cemetery, which Raoul eventually wins, leaving the Phantom with a sword at his throat and at Raoul's mercy. Just as Raoul's about to kill him Christine pipes up, pleading with him not to - or at least, "Not like this." You'd expect: that Raoul, while bowing to the wishes of his beloved fiancee, would also point out that that this version of the Phantom has already killed two people that they know of (one when he hadn't even hit puberty!) has proven himself to be deceitful and manipulative to the max, and is hardly going to leave them alone just because they spared his life. You would then expect him to find some way of restraining the Phantom, whether by tying him up or knocking him out, and then deliver him to the authorities to face justice. Instead: ...they just get on the horse and leave him there, furious and swearing revenge on them both. To make matters worse:In the very next scene, Raoul is discussing with the managers how to capture the Phantom - even though he's already had him at his mercy and could have dealt with him then and there!!! (To be fair, though, this is more the script's fault than Raoul's; in the stage version he hatches his plan to capture the Phantom well before the confrontation in the graveyard, and didn't try to kill or capture the Phantom then because he knew there'd be a better opportunity in the future.)
Anthony Hope has made a plan to elope with Johanna in order to get her away from Judge Turpin, who seeks to marry her despite the fact that he's raised her as a daughter, and is making his way to Sweeney's barber shop in order to inform him of the plan. Unknown to Anthony, Turpin is paying Sweeney a visit for a shave so that he can seduce Johanna, and Sweeney has murder on his mind for Turpin. You'd Expect: Anthony would contact Mrs. Lovett and ask if Sweeney had a customer before barging in, or at least take a moment to look through the goddamn window of the shop before busting in. Instead: He busts right into the barber shop, with Judge Turpin right there in the room, in order to inform Sweeney that he's found Johanna and that she has agreed to the plan. Because Judge Turpin is in the room, this means that he has now been informed about it as well, which not only blows Anthony's plan to elope with her straight to hell, but also Sweeney's plan to kill Turpin — and to make matters even worse for them, Judge Turpin then returns home and has poor Johanna sent to Fogg's Asylum for seeking to defy him. And to make things even worse, Sweeney goes from Anti-Hero to full on Villain Protagonist as a result of being denied his shot at vengeance. Way to break it, Anthony.
In the setup for that scene, Mrs. Lovett tells Sweeney to be patient as he plots his revenge. "Soon, love, soon/Hush, love, hush" and all that. You'd Expect: Sweeney would understand that she's advising patience in waiting for Turpin to fall into his grasp. Instead: When Turpin does fall into his grasp that very day, he takes her advice to heart and spends a few minutes giving the guy a proper shave and singing about pretty women, leading to the scene above. "You told me to wait!" he snarls in the next song. Um, yes, Sweeney, she told you to wait for Turpin to come to you, not to waste time once his throat was finally under your blade! He should have been dead and packed away in the crate long before Anthony arrived!
And just to put the icing on the above cake, in the film version Anthony proceeds to barge into the shop again and disrupts another incredibly important moment. Finally, finally, Sweeney and Mrs Lovett are actually talking about themselves! The audience are mere seconds away from hearing them clarify, in front of one another, the exact nature of their relationship. And then Anthony decides he wants to talk to Sweeney. You'd Expect: Anthony to look into the shop, see two characters of opposite genders talking and employ basic politeness and sensitivity, besides remembering the consequences of the last time he interrupted Sweeney. (In case any tropers have forgotten, these include Sweeney screaming "GET OUT! GET OUT!" while brandishing a straight razor). Instead: ... He goes in like a bull in a china shop.
Mrs Lovett is also a major idiot. The Beadle's coming to ask questions, and she's got a kid on her hands who knows far too much? What ''is'' she going to do with him? You'd Expect: Her to put him somewhere that won't make the situation any worse than it already is. Instead: She locks him in the basement: the one place where he's absolutely guaranteed to gather even more incriminating evidence than he has already.
Older Than Feudalism: In the backstory of The Trachiniae, Deianira is nearly raped by a centaur called Nessus. Her husband Herakles shoots him with arrows poisoned by hydra blood. As Nessus is dying, he gives Deianira some drops of blood from said wound and tells her to handle it very carefully -— it's a love potion that will make Herakles' affections return to her should they ever stray. You'd Expect: She'd put two and two together. This centaur has bad intentions towards her. This centaur hates her husband. He's not actually going to give her something helpful. He was shot with poisoned arrows. Love potion = deadly poison. Instead: At a moment when Herakles has fallen in love with another woman (or seems to have), she tries to save her marriage by using the love potion on him. It kills him brutally, slowly, agonizingly. She commits suicide.