Monty opening the door condenses the probabilities of the two unpicked doors in to the one unpicked door. This occurs because Monty only opens a door with a goa

Monty opening the door condenses the probabilities of the two unpicked doors in to the one unpicked door. This occurs because Monty only opens a door with a goat and never the car. In the original three door version you always had a 2/3 chance of winning if you switched because you'd only lose if you correctly picked the car on the original 1/3 pick.