"A human mind is a wandering mind, and a wandering mind is an unhappy mind."

"The ability to think about what is not happening is a cognitive achievement that comes at an emotional cost."

A report of another one of those "happiness" studies. If unhappiness correlates with a wandering mind, is it because a wandering mind makes you unhappy or because it's when you're unhappy with what you're doing that you think about doing something else?