Now the same position just considered—but a couple of moves earlier so you can see how it developed. There are two clues here, neither of them obvious but both visible with careful tracking. The first is the exchange of minor pieces White can initiate with 1. NxB, RxN. Anytime you can perform an exchange like this you want to consider its consequences; in this case it would leave a loose rook where the Black bishop now stands. A loose piece is an important target, so naturally you look for ways to attack it and create trouble elsewhere at the same time—as with 2. Qd2, which both goes after the rook and creates a battery on the d-file and so threatens 3. Qd8+, QxQ; 4. RxQ#. It's a classic case of the last pattern—(d)—in the scheme set out a few frames ago: White combines a threat against a loose piece with a threat against Black's back rank.
After seeing this much it might be tempting to conclude that the idea works, but that's still premature; for ask whether Black has any way to address both threats in the fork. This is especially important when his queen is available for defense, as it has the versatility to defuse widely separated threats at the same time. In this case Black can play his queen to e7, where it guards the rook on b4 and also defends against the back rank threat by preparing to interpose at f8. And now we arrive at the position in the previous frame. White turns from motif (d) to motif (c), finishing with a rook fork. The threat of a back rank mate drives everything in the sequence, though the mate never actually occurs.
Taken together, these last two positions are a good example of the style of thought you want to cultivate: looking constantly for double threats and for exchanges that loosen pieces to make the double threats work; and then looking beyond the first double threat to the next one, including other loose pieces, mating ideas, and so forth. These longer positions are worth going over until the logic of them flows quickly.