Today’s puzzle is about mental fatigue and the grind of a hard-fought world championship between Ding Liren and the challenger Gukesh Dommaraju. Liren played terribly during the period beforehand, leading the chess world to speculate that the young Indian grandmaster might sweep the tournament. The reality was quite the opposite, and both opponents went into the last game with 6 ½ points each, visibly worn out from their fierce battle. In a simplified endgame, Liren with the white pieces blundered so horribly that Gukesh began shaking, seeing his win immediately- for the game and subsequently for the championship. How did Gukesh crown himself as the youngest world champion in history? Black to move and win.