Lesson
White to move. Main line: 1. Rxa7+ Kxa7 2. Qxb7#
Rxa7+ eliminates the rook and forces the black king to capture on a7. The sacrifice is sound because it does not merely remove material: it fixes the king on the precise square required by White’s queen.
Qxb7# then captures the last pawn beside the king. The queen covers a8, a6 and b8, while the bishop on f3 protects b7 along the long diagonal, so the king cannot take the mating queen.
Attraction combinations should be calculated from the destination backward. First identify the square on which the king would be mated, then search for a check or sacrifice that compels it to occupy that square.