This is similar to another, well-known, paradox. Something about a game show, and there are 3 stalls, and one of them contains a car. The game show host opens up one of the empty stalls to show there's no car behind it. You have to guess which one of the other 2 has the car behind it. And there's a way to play it that makes your chances better than 50%.

Anyone got a link to this paradox?

Update: it's called the Monty Hall Problem: https://en.wikipedia.org/wiki/Monty_Hall_problem