Everybody loves a good movie plot twist. Who could forget how they felt when they learned Bruce Willis is already dead in The Sixth Sense? Or that Verbal Kint is Keyser Soze in The Usual Suspects? Or that Tyler Durden and the Narrator are the same person in Fight Club? A well-planned twist can blow viewers away, causing them to reassess everything they've seen in a new light.
Those twists all came at or near the end of their respective movies, though. Much more difficult is to skillfully put one right in the middle. People expect it less, and it can really give them a shake-up. When the film is only halfway over and suddenly something isn't what it seems, there's no way to predict what's going to come next. That's an exhilarating sensation. Directors as varied as Alfred Hitchcock, Jane Campion, and Bong Joon-ho have all pulled it off.