Quote Originally Posted by Evil DM Mark3 View Post
It tends to upset the player who took time and effort to craft careful strategies or delicate plans to find they don't work because the DM has decided to change things, particularly if they weren't told about the change beforehand.
If players have some kind of understandable misconception, or the GM failed to communicate something important out, then the way to go is to offer a retcon or some other recompense.

But if a player wants to make any kind of deep plan, he should consult with his GM. The GM can work out how it would resolve, and can say whether the PC would know things like whether it can't possibly work and if there's an obvious way to make it more effective.