White's bishop on b3 is masked by a friendly pawn. It lacks a suitable target but is aimed toward the Black king's general vicinity. The c4 pawn, which would do the unmasking, can attack Black’s bishop on d6—not bad, but an upgrade of the target would be nice. White goes to work at both ends of the possible discovery. First comes 1. RxB, QxR (improving the target White anticipates for his pawn); then 2. Bxg7, which forces Kg8 (improving the target for the bishop once uncloaked). Notice that if White had started with Bxg7 it would have been foiled by QxB; by playing RxB first, White forces Black’s queen to leave its defense of g7. So now both pieces in the discovery have good targets: c4-c5+ attacks Black’s queen with a pawn and attacks his king with a bishop. Black has to lose his queen for a bishop by moving it to d5. Of course Black also can avoid much of this by accepting the loss of his bishop on the first move without a recapture—a satisfactory result for White.