White looks for captures to consider and sees QxR. All that keeps him from playing it is the queen on h5; if its protection somehow could be eliminated, White would have the game. He has no effective way to threaten the queen. The best he can do is the knight fork Nf6+, but then Black simply plays g7xN. On the other hand, look at the line between Black’s queen and rook. There is one space between them, on g4. White has a rook on the fourth rank. If it could slide onto g4, it would have protection there and Black’s rook would suddenly be loose. Of course Black could just move his queen to f5—but not if he has no time. Perhaps the solution is becoming clear now: put together the ideas just discussed, starting with 1. Nf6+ and the forced reply g7xN. It not only would leave the fourth rank clear for Rg4; it also would clear the g-file of the pawn now there. After that exchange White therefore can play Rg4 with check. If Black plays QxR, White has h3xQ and has won a queen for a minor piece and a rook. If Black instead interposes with Bg7, White has QxR and has won the exchange.