Which square is the focus of operations here? White attacks Black’s knight on e5 with his knight and rook, but the knight is guarded by two pieces as well: Black’s queen and rook. The pressures on the knight seem to be in equipoise, making it safe; to get anywhere you usually need more attackers against a piece that it has defenders. So your next thought should be to disturb the balance by knocking at least one of the legs out from under the target. The way to do this is clear if you look at what other attacks your pieces make. White’s queen is aimed at Black’s rook. Trading a queen for a rook is unattractive under normal circumstances, but here the sacrifice is a means to an end. White plays QxR; Black recaptures QxQ; and now the balance of pressures against Black’s knight has been changed to two White attackers against one Black defender. White plays NxN, and has won a rook and a knight for his queen.

Hey, wait; that doesn’t sound like a good trade. You've exchanged a five point piece and a three point piece for a nine point piece. But remember to consider the position as it will look after the smoke clears and to ask whether you will have a kicker—a fresh tactical strike after the first one has played itself out. This is especially important when you finish a sequence with a knight placed well, as White’s knight would be here on e5, because often such a piece can then administer a fork. Here White threatens Ng6, forking Black’s king, queen, and rook, and discovering an attack against Black’s queen. It's Black's move, of course. But if he tries to defuse these threats by playing QxN, then he loses his queen to RxQ. If he moves his queen out of harm’s way, he must permit the fork; he can't go after the knight once it reaches the forking square, because the bishop on b1 will protect it there.

It gets worse for Black. Once the White knight does reach g6, Black’s king only has one move: Kh7. When the knight then takes the other piece in the fork—the rook on f8—it discovers a check against Black’s king by the bishop on b1. Material calamity is unavoidable for Black.

This position is a great study in the power of a kicker. The removal of the guard here with QxR does look unworthwhile if you stop after just playing out the immediate exchanges that result in your mind’s eye. But if you look for the threats you would be able to play after the pieces are repositioned by the exchange—and especially for any checks you then could give—you find that the original move QxR essentially ends the game.