They should create Skinner boxes to teach people poker. 'Oh, did you fold to the turn raise? Good, have a Snickers bar.' (That's a Mars bar in Europe, I think.)

back to monty hall:
kiwiMark and Lukie both explained it really well. The way Lukie explained it is kinda like somebody folding their equity share in a pot. When the host opens the wrong door and we switch, we get the probability of the wrong door for free.