People tell you what matters through what they explain without being asked.

Unprompted explanation is a strong signal. When someone volunteers detail about a thing nobody asked about, it tells you the subject is live for them: they are proud of it, worried about it, or working something out. The content matters less than the fact that it arrived unrequested.

Notice this rather than treating it as a digression. It is an invitation, whether or not the person knows it. Following it with interest often takes a conversation somewhere far more real than the topic you had been discussing.