There are countless movies that hinge on an obsessively detailed master plot, whether it be the ultimate bank heist or a plan to make Chris Rock president. But sometimes the characters responsible for that plot throw caution to the wind for no apparent reason, endangering (or flat-out ruining) the plans they had so intricately laid and leaving the rest of us to wonder what the hell they were thinking about. It makes for great drama, but baffling logic.
5Inception -- Cobb Blows the Mission for No Reason
Inception is about international fugitive Dom Cobb (Leo DiCaprio) hacking into other people's dreams in order to steal and/or implant information, which the movie explains by finding hilarious ways for Cobb and his team to lie down and sleep next to their targets while connected to a forest of complicated electrodes and somehow still be incognito.
"Just having a nice sleep EKG, nothing strange here."
The movie focuses on Cobb's big final heist, wherein he and his operatives must reach the deepest level of a tycoon's subconscious and implant an idea. This is actually the least complicated part of the film.
Throughout the movie, the big problem lurking below the surface is that Cobb is haunted by the memories of his dead wife, Mal, which threatens to screw up the whole operation. To make sure this doesn't happen, much of the final plan is hidden from Cobb himself. So Ellen Page's character, Adriadne, knows a way into the mind fortress of the tycoon, but Cobb doesn't. It's for their own protection -- if Cobb knows, his memories of Mal will fuck everything up.
Phantom dream women, right?
Once Cobb and his Dream Bandits make it inside the tycoon's subconscious, they get intercepted by a bunch of dudes on snowmobiles trying to keep them out of the mountain bunker where the tycoon's innermost secrets are stored (because without question, this is how everyone's mind is organized). With everything going to hell, Cobb demands that Adriadne tell him the one thing he can't be allowed to know: the way into the complex. This exchange happens:
ARIADNE: I don't think I should tell you. If Mal finds out ...
COBB: We don't have time for this! Did he add anything?
ARIADNE: He added an air duct system that can cut through the maze.
COBB: Good. [points to her radio] Explain it to them.
"Don't explain anything to the audience, though. They like being kept in the dark."
First, Cobb silences her entirely justified objections by shout-screaming "There's no time for this!" Maybe you could justify this if, in fact, they were in a position where they had no way of succeeding unless Cobb knew. But then he doesn't even use that information. He immediately has her tell it to the other members of the team so they can do all that air-duct-scuttling bullshit while he watches through binoculars.
Predictably, Mal appears and shoots one of Cobb's team members, effectively ruining the mission (or at least making it a lot more difficult and confusing). Had Cobb not insisted that Ariadne tell him about the secret way into the base, Mal would never have shown up (because Mal is Cobb's evil subconscious, so she only knows what he knows). There wasn't even any reason to tell him about it, either -- Cobb could've just asked, "Hey, is there another way into the base? There is? Good, tell them about it while I plug my ears and sing 'Black Hole Sun' to myself for a minute."
"Black Hole Sun, dreams are dumb, dreams are duuuuuumb ..."
His "There's no time for this!" outburst is especially ridiculous because he's asking Ariadne to take an extra step explaining everything to him, making the whole thing take longer. She could've just relayed the information directly to the rest of the team in less time than it took to unnecessarily involve Cobb, and they would've avoided the "murderous wife ghost" factor in the process.