It is not just tactics you need to know

This position is from a game I was watching last night. Black looks like he is doing well in this position, and in fact had even given up material to reach it. However he missed an fairly common idea which saves the day for White. Fortunately for him, White missed the idea as well, as I suspect his opponent was not familiar with it either.
Instead of 1.Kc5?? Kxe3 2.Kd6 Kf4 which was played in the game, White could save half a point with 1.g4! Taking on e3 now lets the g pawn run, so Black eventually has to retreat the king to e5, saving the e pawn, and giving White enough time to get the king back into the game.