Why the most meaningful birthdays end with 9, as in 29 and 39

Milestone Birthdays Can Bring Existential Crisis, Study Says
Milestone Birthdays Can Bring Existential Crisis, Study Says

According to research published in Proceedings of the National Academy of Sciences, the year before we age into a new decade, we're more likely to back up and take a hard look at our lives. Year nine, that time leading up to a new chapter, can prompt us to take action, making us more likely to run a marathon, cheat on our partners or even take our own lives.

"Because life transitions tend to prompt changes in evaluations of the self, people are more apt to evaluate their lives as a chronological decade ends than they are at other times."
One of the study's authors told The Washington Post there's something psychological to those particular birthdays.

"They seem big, they seem looming and they seem more important to us than the others. They make us step back and think about how things have been going up until then and how we want them to go moving forward."

The study found people change things for the better or for the worse. It analyzed results from other studies, and crunched statistics from marathon registration, dating website use and suicide rates. They all spike among people about to reach their next decade. (Video via The Guardian)

This even affects purchasing habits - people tended to pay up for expensive things, including life insurance and cosmetic surgery.

The authors say "Being aware of the tendency to do so can help consumers decide if they are making such decisions for the right reasons."

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