John, I was speaking only of a hypothetical second "contestant" who appears when there are only two doors left. If the word "contestant" is misleading, "person" will do.

His odds are different from the first person's, though faced with exactly the same reality: two doors, one car. That may be the most difficult conceptual hurdle for common sense to get over.

The addition of a second person highlights the difference between the odds on where the car is and the odds on someone's finding it, which happen to be identical for the second person but not for the first.(Doesn't it?)

At one moment it makes perfect sense to me. The next, none at all, in spite of Jim's irrefutable chart and The Snail's summary.