Find the kernel of a discovery for Black. His bishop on d6 masks the Black queen’s path up the d-file. Meanwhile White’s queen is loose on d3. If Black can use the bishop to give check, he will be able to play QxQ afterwards. Black thus finds and plays Bxh2+. White is forced to play KxB (or NxB), and now Black takes White’s queen. There were lots of ways to see this move: the three pieces aligned on the d-file were a tipoff; or you might have set out to examine every check, found only Bxh2, and noticed that as a consequence of that move the d-file would be opened—and also seen that White’s queen is loose. Above all, however, study the relationship of the Black bishop and queen here. The most important thing about the bishop in this position is what it masks.