While Looking at Pins

The critical moment when I gained a clear advantage in my last completed ChessWorld correspondence game presents another illustration of using a pin. I attacked the rook on c8 by moving my bishop to a6. Instead of shuffling the rook to a safer square on the eighth rank, my opponent moved it to c7. Now, the pin on the knight nets me a piece for a pawn.

White to move

18.d5!

Elementary. Pile on the pinned piece. Moving the knight loses the rook, and so 18...exd5 19.exd5 Qd6 20.dxc6+-.