Okay, so imagine you're on a game show. There are three doors. Behind one door is a car, behind the other two, goats. You pick Door #1. The host, who knows what's behind each door, opens Door #3 and reveals a goat. Then he asks, "Do you want to switch your choice to Door #2?"

Do you switch? Does it matter? Most people say no, your chances are 50/50 now. But that's not how it works. Your probability of winning actually *doubles* if you switch. Blows my mind every time.