Chrisg wrote: If I start using illusionism, then players can't rely on their own efforts to gather information about the setting, and can't make the best possible decisions. The local ruler might just seem to be a poncy elf with a flaming sword and a bodyguard of 10 elves. But if I'm using illusionism, no amount of investigating or clever ploys will uncover that he is a lich, because I decided that after the players committed to fighting him.
I am not sure i explained myself right or wrong but i feel your examples don't really come into conflict with mine.
I mean the players want to kill the king, I didn't have anything about the king planned so I let them, and come up with some interesting for the story, and then there are ramifications or plot that occurs because of the decisions you made.
The players want to learn more about the king, I have nothing planned about the king so I let the players search around and collect input in which they figure out something about the king, learning that knowledge does something interesting to the story, then there are ramifications or plot that occurs because of the decisions you made. Maybe its kill the king!
What if they discover that the king is a monster through story or through killing him doesn't matter I made the choice up on the spot both times, why would i make him a monster or not a monster is entirely based on whether or not it would make a more interesting story for my players. Do they know? if I am doing it right then they shouldn't care.
I am not trying to cheat people out of choice i am trying to entertain them.
As long as someone is controlling the story and arbitrating the rules there is no such thing as a true sand box.