This is why you’ll try harder at age 29, 39, 49, 59 …

If you are feeling a sudden burst of motivation to tackle a big goal, your age may be the cause. For his new book “When: The Scientific Secrets of Perfect Timing,” author Daniel H. Pink analyzed how people who are in the last year of a decade have more energy and motivation to accomplish extreme and difficult goals.

We try harder in the last year of a decade

Pink cites psychological research that has found that people in the last year of a decade (or nine-enders) — people ages 29, 39, 49, 59, for example — are more motivated to take on big goals like running a marathon for the first time than at any other age. In fact, a first-time marathoner who is a nine-ender is almost twice as likely to compete in a marathon than people at other ages.

In their research, published in 2014, social psychologists Adam Alter and Hal Hershfield found that “people audit the meaningfulness of their lives as they approach a new decade in chronological age,” calling people on this yearlong search for meaning “nine-enders.” When you are taught to mark time in decades, calling life stages “the twenties,” and “the thirties,” it makes sense that you start to plan goals around this temporal boundary.

Confronted with the encroaching end of another decade of life, we start searching for meaning around us. Some of us start exercising more strenuously. Alter and Hersfield found that nine-enders are more likely to sign up for a marathon. If the nine-enders are already marathon runners, they will post a faster time in their nine-ending year than in the two years before and after that age.

Nine-ender motivation is not always good

This nine-ender phenomenon can backfire though when people assess the meaning of their lives and find it wanting. That’s when the hunt for meaning can become a destructive crisis of faith. This reflection can lead people to reassess their values. For example, the researchers found that male nine-enders were overrepresented on an extramarital affair dating site.

In the most extreme crises of faith, people become more likely to take their own life. Looking at U.S. suicide data from the Centers for Disease Control and Prevention, the researchers found that the 2000-2011 suicide rate was “higher for nine-enders than among people whose ages ended in any other digit.”

“When people feel their lives lack meaning in one of these domains they either respond adaptively, by adopting behaviors that increase the likelihood of finding meaning, or maladaptively, by choosing to act in ways that further rob their lives of meaning,” the researchers said.

By the end of a long decade, we see the finish line, and we start assessing what we have accomplished, for better or for worse. This research shows us that time is an inescapable motivator that could be pushing us to make big decisions. We just need to take a step back to make sure they are the right ones.