Back to offense. White has two checks. One is QxN, the other Rxf6. QxN doesn’t win anything because although White also has a bishop trained on d5, the Black knight is defended twice as well by its king and queen. Rxf6 doesn't seem effective, either; it forks Black’s king and queen, but Black simply plays QxR. Put these ideas together, however, and there is a way to make them work after all: you see that Black’s queen is overworked, defending both the f6 pawn and the knight on d5; or you see that after 1. Rxf6+, QxR, Black’s queen suddenly is out of position to prevent QxN+. That little sequence leaves White with a knight and a pawn in return for a rook, which is okay, but the important thing is to keep nudging the analysis forward. Both of White’s moves so far are checks. As long as he is controlling the initiative in this way and pushing Black’s king around, he may have other tactical gains to exhaust. Thus after 2. QxN+, Ke7 (forced—the king’s only flight square), White asks what his next check would be, and since he is working with his queen he naturally is watchful for forks. Thus 3. Qxc5+, forking Black’s king and rook and taking the rook next move. White nets a knight and two pawns.
The point of this case is that sometimes you can't see the full payoff of exploiting an overworked piece by just looking at the first capture you can make; you have to follow through and consider what would become possible from your new position. Here the idea of the queen fork that concludes the sequence is impossible to see in a first glance at the position. It’s something that comes into view as you keep thinking about checks and the enemy king’s resulting movements. The winning train of thought really starts with a willingness to consider Rxf6 even though it appears to lose the rook on the spot. Don’t focus on the immediate material loss; focus on the changes the exchange creates on the board that is left behind—what lines are affected, what checks would be made possible, and what pieces would have been left with less protection than before.