[jasonswett]

The rule is "after the player has guessed a door, open ALL the other doors except the door that was guessed plus one other door".

I think your confusion is because if there are 100 doors then the rule is self-evident. But when there are only 3 doors, the rule of "open all doors except the door that was guessed plus one other" is indistinguishable from "open just one door".

The key is knowing that the rule is the "open all..." rule.

[colmanhumphrey]

That’s not the rule from the question in the link nor in the original game (the game’s rule isn’t quite the same as the classic problem, it’s even messier). Your proposed rule doesn’t uniquely extend the original, it’s just one of the possible generalizations.

[thehappypm]

Sure, but why is the rule “open all”? In Monty Hall, the rule could also be “open half” or “open one” and it would be the same game!