White has a tempting attack against Black’s back rank: Black’s king is trapped in the corner, and White’s queen is poised to move to c8. Should it? The crucial thing to recognize here is that the kernel of a discovery lies on the board—for Black. His rook masks his bishop, which will check White’s king as soon as the rook vacates f2. This is the dominant tactical fact of this position, and it makes Qc8+ a disaster for White; for then Black plays Rf8+—not only blocking White’s check, but winning his queen with RxQ as soon as White takes his own king out of check. White had better play Kh1 instead.