Quote Originally Posted by PhoenixPhyre View Post
* Lying (in DM voice, not in NPC voice): Denies knowledge. If as the DM you tell them something that is false and that without which they would have made a different choice, you've denied them agency. This is different from giving false information when acting as the voice of an NPC. That's normal, and they have ways of learning that. But if you say "You know that X", and X isn't true, you're on dangerous ground.
I think there should be some sort of concession here for incomplete character knowledge. Saying "You have read X in a book somewhere" or "You've heard word on the street that X" is fallible yet potentially useful; not to mention more likely to draw a player into the world. "You know that X" is, in a way, a form of denying agency in that it sidesteps interpretation of facts and knowledge by the player.