Things Your Mom Should Have Told You

Things Your Mom Should Have Told You

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The Defining Decade

Front cover of the book The Defining Decade: Why your Twenties matter and how to make the most of them
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Your 20s matter. 80% of life’s most defining moments take place by age 35. Two-thirds of lifetime wage growth happens in the first 10 years of a career. More than half of us are married, or dating, or living with our future partner, by age 30. Personality changes more during our 20s than at any time before or after.
According to clinical psychologist Meg Jay, researchers at Boston University and University of Michigan examined dozens of life stories, written by prominent, successful people toward the end of their lives. The researchers found that ‘autobiographically consequential experiences’--the circumstances and people that had the strongest influence on how lives unfolded–were most heavily concentrated during the 20-something years.
Jay covers the separate–but interwoven–critical periods that unfold across the twentysomething years and shares what psychologists, sociologists, neurologists, economists, HR execs, and reproductive specialists know about the unique power of the 20-something years She also challenges some media-driven misconceptions about your 20s and shows how common wisdom about the 20-something years is often wrong.
“The twenties are the years when it will be easiest to start the lives we want. And no matter what we do, the twenties are…a time when the experiences we have disproportionately influence the adult lives we will lead,” said Dr. Meg Jay.
“With about 80 percent of life’s most significant events taking place by age thirty-five, as 30-somethings and beyond, we largely either continue with, or correct for, the moves we made during our 20-something years,” said Dr. Meg Jay.
“In the twenty-something years, even a small shift can radically change where we end up in our thirties and beyond. The twenties are an up-in-the-air and turbulent time, but if we can figure out how to navigate, even a little bit at a time, we can get further, faster, than at any other stage in life,” said Dr. Meg Jay.
“The post-20-something brain is still plastic, of course, but the opportunity is that never again in our lifetime will the brain offer up countless new connections and see what we make of them. Never again will we be so quick to learn new things. Never again will it be so easy to become the people we hope to be,” said Dr. Meg Jay.
“Twentysomethings who use their brains by engaging with good jobs and real relationships are learning the language of adulthood just when their brains are primed to learn it...They learn to get along and get ahead, and this makes them happier and more confident. They learn to be forward-thinking before life’s defining moments are in the rearview mirror,” said Dr. Meg Jay.
“And these are supposed to be the best years of my life,” said a 20-something. Dr. Meg Jay said, “In my experience, these are the most uncertain and some of the most difficult years of life. Contrary to what we see and hear, reaching your potential isn’t even something that usually happens in your twenties–it happens in your thirties or forties or fifties. ”
“Some 20-somethings dream too small, not understanding that their 20-something choices matter and are, in fact, shaping the years ahead. Others dream too big, fueled more by fantasies about limitless possibilities than by experience. Part of realizing our potential is recognizing how our particular gifts and limitations fit with the world around us,” said Dr. Meg Jay.
Said a 20-something: “I get hung up thinking I should know if this is going to work out if I’m going to try it. It feels safer not to pick.” Said Dr. Meg Jay: “Not making choices isn’t safe. The consequences are just further away in time, like in your thirties or forties.”
“We imagine that if nothing happens in our twenties then everything is still possible in our thirties. We think that by avoiding decisions now, we keep all of our options open for later–but not making choices is a choice all the same,” said Dr. Meg Jay.
“When a lot has been left to do, there is enormous thirtysomething pressure to get ahead, get married, pick a city, make money, buy a house, enjoy life, go to graduate school, start a business, get a promotion, save for college and retirement, and have two or three children in a much shorter period of time. Many of these things are incompatible and, as research is just starting to show, simply harder to do all at the same time in our thirties,” said Dr. Meg Jay.
“Our 20s are when we have to start creating our own sense of time, our own plans about how the years ahead will unfold. It is difficult to know how to start our careers or when to start our families,” said Dr. Meg Jay.
“It is tempting to stay distracted and keep everything at a distance. But 20-somethings who live beyond time usually aren’t happy. It’s like living in a cave where we never know what time it is or what we ought to do or why, sometimes until it is too late,” said Dr. Meg Jay.
“Most 20-somethings can’t write the last sentence of their lives, but when pressed, they usually can identify things they want in their 30s or 40s or 60s–or things they don’t want–and work backward from there. This is how you have your own multigenerational epic with a happy ending. This is how you live your life in real time,” according to Dr. Meg Jay.
“Our personalities change more during the 20-something years than at any time before or after…Of any time in life, our 20s are our best chance for change…The 20s are a time when people and personalities are poised for transformation. After age 30, our thoughts, feelings, and behaviors remain incredibly stable,” said Dr. Meg Jay.
“The investments we make in work and love trigger personality maturation. Being a cooperative colleague or a successful partner is what drives personality change. Settling down simply helps us feel more settled,” said Dr. Meg Jay.
“A great relationship or a job to be proud of may seem elusive, but just working toward these things makes us happier. Twentysomethings who experience even some workplace success or financial security are more confident, positive, and responsible than those who do not. Even simply having goals can make us happier and more confident–both now and later,” said Dr. Meg Jay.
“In our 20s, positive personality changes come from what researchers call ‘getting along and getting ahead.’ Feeling better doesn’t come from avoiding adulthood, it comes from investing in adulthood,” said Dr. Meg Jay.
“These are the years when we move from school to work, from hookups to relationships, or from couches to apartments. Most of these changes are about making adult commitments–to bosses, partners, leases, roommates–and these commitments shift how we are in the world and who we are inside,” said Dr. Meg Jay.
“For work success to lead to confidence, the job has to be challenging, and it must require effort. It has to be done without too much help. And it cannot go well every single day. A long run of easy successes creates a sort of fragile confidence, the kind that is shattered when the first failure comes along. A more resilient confidence comes from succeeding–and from surviving some failures,” said Dr. Meg Jay.
“Twentysomethings who don’t feel anxious and incompetent at work are usually overconfident or underemployed. People who are especially good at something may have some innate inclination, or some particular talent, but they have also spent about 10,000 hours practicing or doing that thing. Ten thousand hours is five years of focused, full-time work,” said Dr. Meg Jay.
“Confidence doesn’t come from the inside out. It comes from the outside in. People feel less anxious–and more confident–on the inside when they can point to things they have done well on the outside,” said Dr. Meg Jay.
“Real confidence comes from mastery experience, which are actual, lived moments of success, especially when things seem difficult. Whether we are talking about love or work, the confidence that overrides insecurity comes from experience. There is no other way,” said Dr. Meg Jay.

© 2025 Joanne McHugh
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