"The secret of White's failure was that the attempt to continue the attack by playing his bishop to c1 would have unpinned the black pawn and allowed ... f6-f5. But had he not been in a hurry to celebrate a swift victory and had simply withdrawn his bishop into safety with 19 Bb1, then Black's position would have collapsed of its own accord. To withstand the pressure of two united bishops in the adjacent a1-h8 and b1-h7 diagonals is beyond the powers of any grandmaster."