The science of a wandering mind

Smallwood learned that unhappy minds tend to wander in the past, while happy minds often ponder the future.

Psychology was focused on measurable, outward behavior then. I thought to myself: That’s not what I want to understand about my thoughts. What I want to know is: Why do they come, where do they come from, and why do they persist even if they interfere with attention to the here and now?