White has three pieces to work with in trying for mate: a rook on the open h-file; a queen aimed at f8; and a knight on f5, which among other things can be played to e7—suggesting the possibility of Anastasia’s mate, especially since he already has the other half of the pattern (the rook) in place for it. The problem is that Ne7 isn’t yet effective. Black’s rook guards e7, and f8 is open to Black’s king as a flight square. When you are this close to mating with your knight and rook, however, realize that your queen may be expendable and best used to clear obstacles from your path, even if this means giving the piece away. Think about queen checks and their consequences. White’s 1. Qf8+ can be met in two ways. (a) Black can play KxQ. Now look for White’s next possible check and you find only one: Rh8#. (b) Or Black can reply to Qf8+ with RxQ. But now both obstacles to Anastasia’s mate have been removed: it's safe for White to play Ne7, and the king has no flight squares—so it’s mate.