Lesson
Black to move. Main line: 1... Rg4 2. Qxg4 Rxg4 3. Rxf7 Qxe4+
1...Rg4! offers one rook to pull the queen onto g4. After 2.Qxg4, the second rook recaptures and the key defender is gone.
White can take on f7, but 3...Qxe4+ enters with tempo. Black’s queen now attacks the king and the loose pieces while White no longer has a queen to coordinate the defense.
The motif is a useful calculation shortcut: identify which piece holds everything together, then ask whether a capture, exchange or deflection can remove it.