People spend almost 50% of their waking hours thinking about something other than what they are doing, a new study has found.
Furthermore, this wandering of the mind typically makes them unhappy.
According to US psychologists, unlike other animals, humans spend a lot of time thinking about what is not going on around them - contemplating events that happened in the past, might happen in the future, or may never happen at all.
In order to track this behaviour, the psychologists from Harvard University developed an iPhone web application that contacted 2,250 volunteers at random intervals. The app asked the participants how happy they were, what they were currently doing and whether they were thinking about their current activity or something else that was pleasant, neutral or unpleasant.
The participants could choose from 22 general activities, such as walking, eating, shopping and watching television. On average, respondents reported that their minds were wandering 46.9% of the time, and no less than 30% of the time during every activity except having sex.
"Mind-wandering appears ubiquitous across all activities. This study shows that our mental lives are pervaded, to a remarkable degree, by the non-present," explained one of the researchers," Matthew Killingsworth.
The researchers found that people were happiest when having sex, exercising or engaging in conversation. They were least happy when resting, working or using a home computer.
"Mind-wandering is an excellent predictor of people's happiness. 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," Mr Killingsworth said.
The team estimated that only 4.6% of a person's happiness in a given moment was attributable to the specific activity he or she was doing, whereas a person's mind-wandering status accounted for about 10.8% of his or her happiness.
Further analyses conducted by the researchers suggested that their subjects' mind-wandering was generally the cause, not the consequence, of their unhappiness.
"Many philosophical and religious traditions teach that happiness is to be found by living in the moment, and practitioners are trained to resist mind wandering and to 'be here now'. These traditions suggest that a wandering mind is an unhappy mind. This new research suggests that these traditions are right," Mr Killingsworth added.
Details of these findings are published in the journal, Science.