Strikingly enough, that mind-wandering is a cause rather than a consequence of unhappiness is at once jarring and heartening — it suggests that by training our minds to be more fully present, we’d be honing our capacity for happiness, something Eastern philosophy has long maintained. But perhaps the most surprising and most commanding finding is that even when people’s minds wander off to pleasant things, they’re less happy than when they are fully present in the moment.

- The Science of How Your Mind-Wandering Is Robbing You of Happiness | Brain Pickings