Test your intuition with this famous probability puzzle!
When you first pick a door, you have a 1/3 chance of picking the car. This means there's a 2/3 chance the car is behind one of the other doors. When Monty reveals a goat, he's giving you information! The 2/3 probability doesn't disappear - it all goes to the remaining unopened door. So switching gives you a 2/3 chance of winning!