Harvard Happiness Experts, Dan Gilbert and Matthew Killingsworth conducted experiments and found,

People spend 46.9 percent of their waking hours thinking about something other than what they’re doing, and this mind-wandering typically makes them unhappy… “Mind-wandering is an excellent predictor of people’s happiness,” Killingsworth says. “In fact, how often our minds leave the present and where they tend to go is a better predictor of our happiness than the activities in which we are engaged.”… Time-lag analyses conducted by the researchers suggested that their subjects’ mind-wandering was generally the cause, not the consequence, of their unhappiness.

Do you have a wandering mind?

Try training your attention on your breath as it moves in and out of your nostrils for one minute.  When your mind wanders, bring it back to your breath at the nostrils.   The more you train your mind to stay present with the breath, the less your mind wanders!