Most of us think all day and almost never look at what we're thinking. Some of it is plainly useful: the appointment at ten, the bread to buy. But slipped in among those are other thoughts. Replaying a conversation that's already over. Guessing what someone meant. Worrying about something you can't touch. Holding on to what someone did years ago.
That second kind feels like work, but it isn't. It circles back and solves nothing, and it leaves the mind running faster and more tired. Each thought also leaves a trace, and the more often one repeats, the deeper the groove it wears.
The hard part is that these thoughts rarely announce themselves. They arrive dressed as concern, or fairness, or planning. A more useful question than 'is this true?' is 'is this going anywhere?' The first step is only to notice which kind you're having: useful, wasted, negative or positive.