ok, let's use an extreme example here:
let's say you get to pick from 1000 doors. Only 1 door has a prize behind it. Now, you select a door. The odds are 1/1000 that you have the correct door (really crappy odds). Now I ask you the question: do you have the right door? Odds are that you don't. That's essentially what's happening here except they're doing it with a switch instead of a question.
as far as the envelopes, if you added that there were 40 or 50 guys with a pair of envelopes, should you always or never switch, that's a different question.
let's say you get to pick from 1000 doors. Only 1 door has a prize behind it. Now, you select a door. The odds are 1/1000 that you have the correct door (really crappy odds). Now I ask you the question: do you have the right door? Odds are that you don't. That's essentially what's happening here except they're doing it with a switch instead of a question.
as far as the envelopes, if you added that there were 40 or 50 guys with a pair of envelopes, should you always or never switch, that's a different question.