Rook Endings: Lasker 1925
I love finding Endgame positions which look almost identical, but a subtle difference gives a totally different result.
I hit upon these two positions by Emmanuel Lasker composed in 1925 (positions 22 and 23 from the Encyclopadia of Chess Endings Rook Endings Part 1).
POSITION 1: Black to Move (White is winning)
POSITION 2: Black to Move (Drawn)
Why does the position of the White Rook on h7 vs g7 matter?
To avoid mate, Black's King can either head to c8 (short side) or e8 (long side).
The key idea for Black to attempt to draw comes down to "King on the short side, Rook on the long side".
By heading to the short side, the defensive Rook will aim to check the White King horizontally. In this way, the Black King does not interfere with the Black Rook's checks.
The White King will wants to stop the horizontal checks by heading towards the Rook, but yet can't drift too far from the d-pawn.
The Black Rook wants to be able to check horizontally as far away as possible from the White King. Hence it wants to get to the h-file, and not the g-file where it is too close.
POSITION 1: Black to Move (White is winning) Annotations
Observe how Black's Rook can now obtain the h-file and thus be far enough away from the White King.
Instructive Mistakes: Why can't the Black King go to the long side in Position 2?
With knowledge of Position 1, White is able to regain control of the h-file.
Exceptional presentation of Rook Endgame essential knowledge are the chess.com 10 part videos by IM Daniel Rensch at