The Game Master should try to be as objective as possible (most of the time). Specifically, when he has knowledge that the characters he's managing, the NPCs, don't have. An intelligent enemy with some basic facts? Sure, they could anticipate the adventurers' moves - it's possible - but do they? Well, that's usually a judgement call.
So, how would you decide if those cunning NPCs figure out what the PCs are doing? With this fancy new table I just created, of course!
Does the enemy know their plans?
1. Yes, they do. And it didn't take long for them to figure it out.
2. Not exactly, but they're close. With a little more information, they'll know what the PCs are up to.
3. The enemy's expectations are well removed from what the PCs are attempting.
4. Diametrically opposed. The NPCs are absolutely sure the PCs are going to zag right, when really, their zigging left.
Authored by Venger Satanis