Start by observing that White has the makings of the Greek gift sacrifice and follow-up. Assume play goes 1. Bxh7+, KxB; 2. Ng5+, Kg8; 3. Qh5 (later we will consider other possibilities). All right; now what? You might be looking here to win Black’s queen (plus a pawn) for your knight and bishop after he plays QxNg5, but before you can expect that sacrifice from your opponent you have to know that without it you have mate. Black’s best move other than QxN would be 3. …Re8, making room for his king to flee after White plays Qh7+. So study the position and see whether you will be able to pin down the king or whether it will escape from there. The answer is that you will be able to mate using the sequence described in skeletal form in the previous frame. Again, you start by taking the queen to f7, not h7: 4. Qxf7+, Kh8; 5. Qh5+, Kg8; 6. Qh7+, Kf8; 7. Qh8+, Ke7; 8. Qxg7#.
The point: White does threaten mate here, so Black will need to sacrifice his queen with QxN to stop him.
With a little practice you should be able to picture all this from the starting position shown here; and when you do, you can congratulate yourself for being able to see eight moves ahead. It isn’t so difficult when you are working with a familiar pattern. Notice again the key roles played by the pawn on e5 and the queen on d8. Without those pieces in place you still might be able to eventually hunt down the king or collect material, but the immediate quest for mate fails.