A ladder is a promise of many moves, not one: atari, forced extension, atari again — a zig-zag chase that must hold all the way to the edge. Read the whole path before starting, because one friendly stone on the escape route is a ladder-breaker that flips the result. Here three of your stones already crowd the white one, and only one of its two liberties begins a chase your stones can keep tight; the other points it at the open board, where every extension gains liberties. Start the chase from the side your support protects.