Time. Time is critical（决定性的） because how you spend the hours of your days sum（概括） up to the years of your life. I'm a professor of happiness and I study time, which is kind of ironic（说反话的） because for my own personal happiness, time proved to be the single biggest barrier（(阻碍通道的)障碍物）. I remember one day earlier in my career when I was an assistant professor at Wharton, I had traveled up to New York to give a talk, and that day, like so many, it was just crazy hectic（脸上发红）. My presentation was sandwiched between back-to-back meetings from which I'm rushing（冲） to this colleague dinner and then frantically（匆忙地） rushing（冲） to the train station to catch the very last train that would get me home to my four-month-old and my husband asleep in Philly. Now, I did make（使） the train that night, but I remember so vividly sinking into my seat, totally exhausted（排出）, and resting my forehead against the glass, watching the nightlights whisper（低声地讲）, "I don't know if I can keep up."

  Between the pressures of work, wanting to be a good parent, wanting to be a good partner, a good friend, the never-ending pile（堆） of chores（杂务）, there simply weren't enough hours in the day to get it all done, let alone do any of it well, let alone to enjoy any of it along the way. And I wanted more time, not just so I could get more done, I wanted more time so that I could slow down and actually experience the hours that I was spending so that my entire（全部的） life wouldn't end up passing me by in this blur（模糊不清的事物）. I know now that what I was experiencing is time poverty, which is defined as the acute（敏锐的） feeling of having too much to do and not enough time to do it. Even if you haven't heard this term before, I suspect（怀疑） you know exactly what I'm talking about. Show of hands, how many of you agree with this statement, "I never seem to have enough time to get everything done?" A lot of us. And we're not alone.

  My research team conducted（指挥） a national poll（投票） that showed that nearly half of Americans feel this way, and it's not just us in the U.S. Folks across the globe（地球） report suffering from a hectic（脸上发红） pace（步） of life with too little time. And on that night on the train, when I felt very time poor and not happy, I concluded that there was one obvious solution. I needed to quit my job and move to a sunny island somewhere. Because with all the hours of my days to relax and spend doing what I wanted, then surely I'd be happier. I was like, "Is that true? Are people who have a whole lot more time in fact happier?" And this is an empirical（完全根据经验的） question and one that I could test and probably should test before telling my boss that I quit and my husband that we should pack for life at the beach.

  So I recruited（ 征募） a couple of my favorite collaborators（ 合作者） and together we examined what's the relationship between the amount of discretionary time people have and their happiness. And across our studies, including an analysis of the American Time Use Survey, which captures（捕获） how tens of thousands of working as well as non-working Americans spent a regular day, we found a consistent（坚持的） pattern of results. And it looked like this. It was an upside（优势）-down U-shape, like an arc（弧（度）） or a rainbow. Now this is interesting because it shows that happiness goes down on both ends of the spectrum（光）. Yes, people with too little time, those with less than approximately two hours of discretionary time in the day were less happy.

  But this didn't surprise me because I knew all about the high level of stress that comes from being time poor. It was this other side that was surprising. Those with more than approximately five hours of discretionary time in the day were also less happy. And this is interesting because it shows there is such thing as having too much time. But how could that be? How could having loads（负载） of hours to relax and spend however you want to be associated（交往） with less happiness?

  Well, it turns out we are driven to be at least a little productive（能生产的）. Research shows that people are adverse（不利的） to being idle（空闲的）, and so when we spend all the hours of the day, day in, day out, with nothing to show for it, it undermines（破坏） our sense of purpose. And from that, we feel less satisfied（感到满意的）. This is important to note because it cautions us on those days that feel so hectic. The answer isn't to quit everything and move to life, you know, sitting in a beach chair.