White’s knight is on the same color square as Black’s king and queen and can fork them at f7. Black protects the square with his rook. If White tries to start by taking out the rook with his queen, Black recaptures with his own queen and the fork is spoiled. If White plays QxQ, however, Black replies with RxQ, and now the fork works, winning White a rook. Yet with king and queen positioned like this it would be rash to settle for a rook; consider what happens if White simply goes ahead with 1. Nxf7+ and allows his knight to be captured by RxN. Now Black's queen is left loose for the taking with QxQ, which mates a move later (after Black gives a futile interposition with his rook). So the fork 1. Nxf7+ works after all, as the lesser evil for Black is letting his queen be taken by White’s knight—after which Black recaptures with his rook, allowing White to then play QxR+. White ends up with a queen and a rook against Black’s two knights, an easy win from here.