The overloaded defender

Black’s rook on c7 has two jobs: protect h7 from mate and guard the rook on c8. White proves that one rook cannot do both.

Lesson

White to move. Main line: 1. Qxh7+ Rxh7 2. Rxc8+ Kg7 3. Rc7+

1.Qxh7+! forces the c7-rook away from the back rank. Declining the queen is not an option because the king is in check.

Once the defender lands on h7, 2.Rxc8+ wins the other rook. White has exchanged a queen for two rooks and kept the initiative with another check.

An overloaded defender is not merely attacked twice; it is assigned two incompatible tasks. A forcing move against either task makes the other one collapse.