Rook vs Pawn: The Knight Promotion Trick

One of the most instructive shocks in the endgame is that an extra rook can be worth only a draw when the enemy pawn is one square from promotion and shielded by its king.

Why there is no win. Capturing the defended pawn just strips the board bare, and nothing else stops it. The most you can do is Rh2+ followed by Kc3, forcing Black to commit.

Queen loses, knight holds. Promote to a queen and Rh1+ kicks the king off the first rank and collects it. Promote to a knight and it arrives on b1 with check, and from b1 it has a3 to shuffle to. Rook against knight is a theoretical draw.

The corner is the difference. A knight that lands on b1 is safe. A knight that lands on a1 is trapped, which is exactly what the companion position shows.

Keep the knight next to the king. Once you promote, do not let the knight wander. In rook against knight the lone knight gets hunted down, so keep it glued to its king. Na3 stays home; a stray hop like Nb5 loses it.

The strategic consequence. This trick works for every pawn except the rook pawn, and that changes how the whole ending is played. Driving the defending king down from behind is pointless: he underpromotes and holds. The attacker has to come around from the side instead, and the outflanking positions show exactly how.