Checkmate ends the game immediately, provided the move producing it was legal (Art. 5.1.1); Resignation: a player who resigns loses immediately, unless the position is one in which the opponent cannot possibly checkmate (Art. 5.1.2); Time: a player who does not complete the prescribed moves in th...
Why people argue about this
People often assume that if a player resigns during their opponent's move, they lose immediately without considering whether it would have been possible for them to win with optimal play. Actually, the resignation only results in a loss if no checkmate is feasible from the current position. This rule can lead to misunderstandings about when and why a game ends due to resignation.