Emma Seppala tweeted it:

First of all, people’s minds wander a lot. Forty-seven percent of the time, people are thinking about something other than what they’re currently doing. Consider that statistic next time you’re sitting in a meeting or driving down the street.

...

As it turns out, there is a strong relationship between mind-wandering now and being unhappy a short time later, consistent with the idea that mind-wandering is causing people to be unhappy. In contrast, there’s no relationship between being unhappy now and mind-wandering a short time later. Mind-wandering precedes unhappiness but unhappiness does not precede mind-wandering. In other words, mind-wandering seems likely to be a cause, and not merely a consequence, of unhappiness.

How could this be happening? I think a big part of the reason is that when our minds wander, we often think about unpleasant things: our worries, our anxieties, our regrets. These negative thoughts turn out to have a gigantic relationship to (un)happiness. Yet even when people are thinking about something they describe as neutral, they’re still considerably less happy than when they’re not mind-wandering. In fact, even when they’re thinking about something they describe as pleasant, they’re still slightly less happy than when they aren’t mind-wandering at all.

The lesson here isn’t that we should stop mind-wandering entirely—after all, our capacity to revisit the past and imagine the future is immensely useful, and some degree of mind-wandering is probably unavoidable. But these results do suggest that mind-wandering less often could substantially improve the quality of our lives. If we learn to fully engage in the present, we may be able to cope more effectively with the bad moments and draw even more enjoyment from the good ones.

There's a lot more good stuff in the article:

http://greatergood.berkeley.edu/article/item/does_mind_wandering_make_you_unhappy

Also watch Matt Killingsworth's TED Talk, "Want to be happier? Stay in the moment."

From "Barking Up The Wrong Tree":  

"The researchers estimated that only 4.6 percent 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 percent of his or her happiness.

Time-lag analyses conducted by the researchers suggested that their subjects’ mind-wandering was generally the cause, not the consequence, of their unhappiness."

Read more: http://www.bakadesuyo.com/2012/03/why-do-we-daydream-is-it-good-for-us/#ixzz2bDzDXxXm

Some mind wandering is inevitable, but the more it happens, the more the person isn't living in the moment.

Mind wandering also makes you more creative:

http://www.bakadesuyo.com/2012/12/wandering-mind-path-creative-genius-misery-early-death/

It's never easy and clear cut. Every emotion we have has a benefit and a downside. 

Feeling powerful improves performance - and makes you more likely to cheat. 

Feeling happy makes you pleasant to work with - it also makes you less detail oriented.

We should not always live in the moment any more than we should always let our minds wander. 

We need both, at the right times. 

And that's why life can be such a challenge.

The more I live, the more I realize that timing matters.

Right thing at the right time makes a big difference.