The idea here will be familiar from the other positions in this chapter, but we'll talk it through from scratch. Sometimes a little knot of pieces that attack each other like those in the middle of the board here can seem confusing. Just take it apart with first principles. First, glance at the Black king’s lines and notice the pin of Black’s rook by White’s queen; then methodically diagnose the pin and its prospects. A first question about almost any pinned piece is whether you can attack it more times than it’s defended. Here the pinned rook is attacked once and defended once, so ask whether White can attack it again. Since the target is on a light-squared diagonal, White could add an attacker by playing his f3 bishop to g4. But this doesn’t work because then Black can play QxQ; after White recaptures NxQ, Black moves his rook to safety. The point: White's bishop's can't be swung into action against the rook so easily; it is doing important work on f3.

The problem for White is that Black’s queen not only guards the pinned piece but attacks the pinning piece. For White to get anywhere he therefore will have to work with violent, forcing moves that don’t give Black time to exchange queens and destroy the pin. When in doubt, consider exchanges. Here the only piece White can use to perform a capture is his queen. He has QxR+. And then what comes after Black recaptures QxQ? Bd5, which takes advantage after all of the bishop’s ability to travel the light squares. This pins and then wins Black’s queen with support from the knight on c3.

It’s another example of a recurring principle: if you are stuck for ways to bring more firepower down on a pinned piece, consider taking it and ask whether doing so would free the way for you to bring in more reinforcements. Another way to put the point is that White does have two pieces he can use to attack the pinned position here; it’s just that he just needs to use them to attack sequentially rather than simultaneously.