At a end of a session, a player had to pick one of three nominally identical curtains. The player could then switch. Compare this to a feature of the Millionaire. Picture this scenario. Liz gets a question and four possible answers.
Most folks think the odds are the same either way on either show.
On Let's Make a Deal, switching is better. The chance of the initial choice being right is one out of three. It's twice as good, two out of three, for the unopened unselected curtain. The contestant began with one of three indistinguishable curtains. The chance it was right was one out of three.