Most of the time the line between player and character is blurred. So blurred, in fact, that many times the GM has to specifically tell the player their character wouldn’t have knowledge of a certain situation.
The road goes two ways, though. There are many times as a GM that you know information about the players’ plans that the NPCs wouldn’t know, and can use that to tweak the NPC actions to better balance the game, give the players a break if they are way over their heads (or punish naughty players who get themselves into bad predicaments), or get the story back on the rails. The major difference is that as the GM, you are running the game, so the majority of the time the players are never the wiser to your subtle manipulations.