Familiar idea, different direction. A fianchettoed bishop on b2 or g2 (or the equivalent squares on Black's side of the board) often is easy to mask and unmask with an advancing pawn; here, with a pawn on c3 in front of White’s b2 bishop, White has tremendous potential energy on the long diagonal, and Black plays there at his peril. In this simple position both parties to the discovery have open lines to good targets: c3-c4 unmasks BxQ and attacks—and wins—Black’s bishop on d5.