What's the One Plot Twist That Never Gets Old?

Plot twists are supposed to startle us by coming out of nowhere, but we see the same kinds of twists again and again. (The hero was actually the villain! The monster is on the ship! Actually they're ghosts!) Still, some plot twists never feel worn out. Which one gets you every time?

Please include examples from movies, books, comics, or TV — and show us a picture or video to spice up our Friday afternoons.