The loudest fact on the board is White’s passed pawn at c7. It threatens to promote if Black moves his rook, so Black looks for ways to rid himself of it. He can’t take the pawn with his rook because then White plays NxR. But Black could play Bxc7. Then White's NxB is met with RxN. Look good? No, for imagine the board after that first capture you are contemplating and ask not only whether your piece could be retaken but also whether you would have inadvertently created a tactical opening for your opponent—here, by lining up two of your pieces to be pinned: Bxc7 leaves Black’s bishop adjacent to his rook on the c-file. As soon as you see this, worry about whether White can run one of his pieces through both of yours. He can indeed, with Rc6. Then if Black moves his bishop, White plays RxR; notice that Black’s rook is loose. Yet if Black moves his rook, White plays RxB. And if Black moves neither piece, White still plays RxB, with the knight providing cover for the rook. So White’s pawn cannot safely be taken after all. (Black’s best move probably is Bd4, moving his bishop out of danger.)