As soon as I saw the move on the board, it made perfect sense. But my friend (who is also a master) and I hadn't predicted it while quickly playing through the game solitaire chess. I think this is a perfect example of a strong positional forcing move.
I wanted to share news of a very interesting new book: "Modern Chess: From Steinitz to the 21st Century" by International Master Craig Pritchett. This Thinkers Publishing title is exactly what it sounds like, and has something for chess enthusiasts of all levels: Some history, some culture, some famous games we ought to have seen but maybe haven't, some instruction.
Before every move, you must consider all of your opponent's possible forcing replies to your move! When I was 16, I thought I had 'discovered' this key to avoiding silly tactical mistakes in OTB games. Later, when I became a chess teacher and coach, I discovered that many instructional books wisely direct readers to critically examine all the possible checks, captures and threats for both sides.