Figure[White to move]

Here is another study in failure. The elements of a back rank mate seem to be in place: Black’s king is trapped behind its pawn cover, Black has no defenders on the back rank, and White has a battery of queen and rook on the e-file. Yet the attack comes up short because after White plays Qe8+ Black can interpose his queen at c8. Since Black’s queen is then protected by his king, White has no way to penetrate the position. The sequence still is fine for White; it successfully eliminates the pressure on his king (specifically the threat of Qa4#). It just doesn’t produce mate.