Endgames Are a Different Sport
The endgame is a different sport. Not a different phase of the same sport, a different sport, with different rules, that happens to use the same board.
In the opening, everything is about ideas: territory, threats, pieces you do not have yet, the fear of being outnumbered on the wrong wing. Twenty moves later the questions have become arithmetic. Where does the king go, which pawn is the passed one, is the rook behind it or in front of it, and does the other fellow know. The endgame has almost no imagination in it. It has arithmetic, and nerve.
I have been studying one long ending all summer. Two rooks and a pawn against a rook, technically winning for years, and the game went on for seventy moves. Both players knew the ending table; both players knew that the win was somewhere in the middle of the position and not at the end of it. What kept the game alive was not the play, which was mostly correct, but the tension of the walk. Every move was a small risk taken for the sake of the next move.
What I took from studying it was not a tactic. It was the observation that most endgames are lost before the endgames begin, in the middlegame, by people who have grabbed a pawn and not thought about the square their king was standing on. Every table of endgames is full of wins that were thrown away in the last ten moves of a long game, by a player who had three hours to think about it and did not spend two minutes doing so.
The endurance of it is the other lesson. Endgame technique is easy to acquire and requires a kind of calm that is not the same as calculation. You must be willing to be a little worse and then a little worse again, in public, for an hour, while the person across the table thinks the same thing. Chess ends differently from the way it begins, and a player who has only ever played the first part is learning a second language late.
So I have taken to playing out whole endings in my head, not the famous ones but mine, and the first thing I have learned is that I resign them too early.