Social psychologists describe this change as a consequence of a gradual shifting from promotion motivation -- seeing our goals in terms of what we can gain, or how we can end up better off, to prevention motivation—seeing our goals in terms of avoiding loss and keeping things running smoothly. Everyone, of course, has both motivations. But the relative amounts of each differ from person to person, and can shift with experience as we age.
Research from Northwestern University in the journal Psychology and Aging suggests that promotion-mindedness is most prevalent among the young, because youth is a time for focusing on your hopes for the future, what you ideally want to do—you don't have much in the way of responsibilities, and you still believe you can do anything you set your mind to. That and you think you are immortal. This is more or less a recipe for strong promotion motivation.
As we get older, illusions of immortality vanish. There is a mortgage that needs to be paid, a home that must be maintained, and children to be cared for. (Speaking of children, new mothers are an especially prevention-minded group. They have the daunting task of somehow protecting a completely vulnerable, clueless, yet hell-bent-on-exploration infant from a world filled with germs, stairs, pointy objects, and electrical outlets. New motherhood is mostly about ceaseless vigilance.)
The older we get, the more we want to hang on to what we've already got—the things we've worked so hard to achieve. We also have more experience with pain and loss, having been knocked around a bit by life, and having learned a few lessons the hard way.
In a recent set of studies, psychologists Cassie Mogliner, Sepandar Kamvar, and Jennifer Aaker looked for evidence of how our sense of happiness changes with age by analyzing twelve million personal blogs. Specifically, they were interested in seeing what kinds of emotions the bloggers mentioned when they talked about feeling "happy."
They found that younger bloggers described experiences of happiness as being times when they felt excited, ecstatic, or elated—they way you feel when you are anticipating the joys the future will bring - like finding love, getting ahead at work, or moving to a new town.
Older bloggers were more inclined to describe happy experiences as moments of feeling peaceful, relaxed, calm, or relieved—they way you feel when you are getting along with your spouse, staying healthy, and able to make your mortgage payments. This kind of happiness is less about what lies ahead, and more about being content in your current circumstances.
(You can see these age-related differences in motivation very much reflected in the workplace, where older workers have more prevention-motivated concerns - like job security and flexible work schedules, while people under thirty have more promotion concerns—like opportunities to develop skills.)
If you're like me, and you find that your life has become more about pursuing peace and relaxation than giddy excitement, rest assured that you aren't missing out on happiness. Your happiness has evolved, just as you have. Even though our version seems less fun by the standards of our younger selves, that doesn't mean it's less good.