What Black pieces are loose? Really just the bishop on d1; notice how Black’s knight is protected by the Black rook against capture by White’s rook. How can White attack the bishop? With Rd3. To make that move interesting, another loose piece needs to be lured elsewhere onto the d file. The Black knight is the only real candidate. Ask what the knight protects on the d file that you might attack. Seemingly nothing—but maybe you can get the knight onto the d6 square by making trouble there with a pawn advance toward promotion (and the two exchanges that naturally follow): 1. d5-d6, c7xd6; 2. c5xd6, Nxd6; and now 3. Rd3 forks the bishop and knight. Black might see this and postpone Nxd6, first playing RxR; Black is thinking that after White recaptures with f2xR, Black can play Nxd6 without fear of being forked. But White doesn’t reply to RxR by recapturing. He moves his d-pawn to d7 and now it can’t be stopped from promoting. Black is better off putting up with the fork after all.