There are exceptions

Black to play

While rules can get us pretty far in chess, there are always exceptions we need to be aware of. In the diagrammed position White assumed he had an easy win, which resulted in him dropping half a point.
In the position is is Black's move. White's idea was to create a passed pawn on the Queenside after b4-b5 and then clean up the kingside pawns. However the plan unravelled after 1. ... f3+ (exchanging on g3 does lose for Black) 2.Kd2 Kd4 3.b4 Kc4 4.b5 axb At this point White went in to a deep think, as he realised that his original plan goes badly wrong after 5.axb Kxb5 6.Ke3 Kc4 7.Kf4?? Kd3 8.Kxg4 Ke2 and Black will promote well ahead of White. So instead he bailed out with 6.Kd3 Kb4 7.Kd4 Kb3 and a draw was agreed.
There is a slightly trickier line that White might have tried 5.a5 Kc5 6.Kc3 but after 6. ... b4+ 7.Kb3 Kb5 8.a6 Kxa6 9.Kxb4 Black will still be able to get to e2 if White goes after the g4 pawn.
If White wanted to try for a win it turns out he has to break the "push the potential passed pawn" rule that often applies. Instead of 3.b4, 3.a5! is the winning move. White then pushes the Black king far enough back on the queenside so that when the exchange on b5 happens, the king cannot get back to e2 in time.