A hole-in-one: the ball goes from the tee into the cup with a single stroke. Aces almost always happen on par-3s, where the green is reachable in one, and they're a genuine lightning strike — the odds for an average amateur are usually put around 12,500 to 1 on any given par-3. There's real luck involved (plenty of terrible swings have made aces), which is part of the charm. Tradition says the golfer who makes one buys drinks for the group afterward.