2024/05/20 DPA: "I Spy...A Hanging Piece"

Black to move.

Material is even.

White's back rank seems adequately defended.

1. ... Ng4, threatening 2. ... Qxh2+ and 3. ... Qh1#, fails due to 2. fxg4.

1. ... Rxd2 doesn't do anything.

After somehow thinking Black could play 1. ... Ng4 and then 2. ... Qd4+ by moving through the pawn on g4 but winning back the piece, I realized that I didn't need the Knight:  1. ... Qd4+ attacks the King and adds a second attacker of the Bishop.

White would love to block with the Bishop but that loses also.

.

The key was recognizing the dual-purpose of 1. ... Qd4:  the check and the 2nd attack of the Bishop, which is defended only once.

As a thought experiment, look what happens when the light-squared Bishop is not there:  now 2. Be3, blocking the check and removing the Bishop as a target, works because the Bishop is defended by the Rook.

In this case, the dual-purpose attacking move was met with a dual-purpose defensive move.  When I watch GM games, they frequently make dual-purpose moves.