Well, if I were a player in a game, and I used my in-game resources (divination, etc.) to learn about the setting, I wouldn't expect "GM Authority" to prevent me from doing so, either.
If I decided my character would go left, and the GM just decided to move whatever was to the right to the left, I would be a bit miffed were I to discover it (and if I went back, and tried to go right, there is some chance that I would!).
DM authority can also decide to have the Tarrasque teleported in to face 1st level PCs, but that doesn't make it a good idea.
RC