Chess is more than a game or a mental training. It is a distinct attainment. I have always regarded the playing of chess and the accomplishment of a good game as an art, and something to be admired no less than an artist's canvas or the product of a sculptor's chisel. Chess is a mental diversion rather than a game. It is both artistic and scientific.
The great World Champions Morphy, Steinitz, and Lasker were past masters in the art of Pawn play; they had no superiors in their handling of endgames. The present World Champion has not the strength of the other three as an endgame player, and is therefore inferior to them.
When you sit down to play a game you should think only about the position, but not about the opponent. Whether chess is regarded as a science, or an art, or a sport, all the same psychology bears no relation to it and only stands in the way of real chess.