Book Review: The Defining Decade by Meg Jay, PhD

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  • Title: The Defining Decade
  • Sub-title: Why Your Twenties Matter And How To Make The Most Of Them Now
  • Author: Meg Jay, PhD
  • About the author: Meg Jay, PhD is a clinical psychologist specializing in adult development and twentysomethings. She has a private practice in Virginia and is also an assistant clinical professor at the University of Virginia. She received her doctorate from UC Berkeley.
  • Pages: 272
  • Published: 2013
  • Link to book


The Defining Decade is all about the most pivotal decade in everyone’s lives: the twenties.

Author Meg Jay, PhD is a psychologist that specializes in adult development with a focus on twentysomethings.

In over two decades she has worked with a countless number of twentysomethings either as her clients or students.

In her book, she shares what she learned from these interactions. Her goal is to dispel myths and share eye-opening advice about the twentysomething years. This decade is filled with many defining moments , which Meg dives deeply into.

The book’s division into three parts (work, love, and mind and body) provides for a comprehensive coverage of one’s most important areas of life.


I would recommend this book to those in their twenties, those about to enter their twenties, and parents of twentysomething children.

I read this book at age 26 and still found it valuable. With six years of my twenties down, I can tell you that this book would have woken me up to reality if I had read this at 20.

Your twenties zoom by, and if you aren’t prepared and taking advantage of them, you’ll be 30 before you know it. The author emphasizes this in different ways throughout the book.

Check out this related reading next!


  • In no particular order

1. Your twenties matter. 80% of life’s most defining moments take place by 35. Two-thirds of lifetime wage growth happens in the first 10 years of a career. Personality changes more during our twenties than at any time before or after.

2. In almost all areas of development, there is a critical period, a time when we are primed for growth and change. The twenties are that critical period of adulthood.

3. The postmillennial midlife crisis is figuring out that while we were busy making sure we didn’t miss out on anything, we were setting ourselves up to miss out on some of the most important things of all.

4. Identity capital is our collection of personal assets. Identity capital is how we build ourselves—bit by bit, over time. Twentysomethings should take jobs with the most capital.

5. “The Strength of Weak Ties:” Weak ties are the people we have met, or are connected to somehow, but do not currently know well. Information and opportunity spread farther and faster through weak ties than through close friends because weak ties have fewer overlapping contacts. See: 20 Tips on How to Build Your Network in College

6. New things almost always come from outside your inner circle. People are willing to help others because of a “helper’s high” that comes from being generous.

7. Many twentysomethings are raised hearing—“Follow your dreams!” “Reach for the stars!”—but often don’t know how to get these things done.

8. It’s easy to let life pass. It’s easier not to know, not to choose, and not to do. When we make choices, we open ourselves up to hard work, failure, and heartbreak.

9. 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.

10. Twentysomethings who don’t get started wind up with blank résumés and out-of-touch lives only to settle far more down the road.

11. If the first step in establishing a professional identity is claiming our interests and talents, then the next step is claiming a story about our interests and talents, a narrative we can take with us to interviews and coffee dates.

12. Many of the author’s twentysomething clients either don’t take their relationships seriously or don’t think they are allowed to. Then somewhere around thirty, getting married suddenly seems pressing.

13. Be “in like” with someone you choose to be in a relationship with. This means being alike in ways that matter and genuinely liking who the other person is. They are qualities you feel are non-negotiable.

14. In our twenties, the pleasure-seeking, emotional brain is ready to go while the forward-thinking frontal lobe is still a work in progress. The frontal lobe is still developing until your mid-twenties.

15. The post-twentysomething brain is still plastic, of course, but the opportunity is that never again in our lifetime will the brain offer up countless new connections. Never again will we be so quick to learn new things. The risk is that we may not act now. See: How to Learn More and Learn Faster: 20 Things to Do

16. 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.

17. Compared to older adults, twentysomethings find negative information more memorable than positive information. There is more activity in the amygdala—the seat of the emotional brain. When twentysomethings have their competence criticized, they become anxious and angry.

18. People feel less anxious—and more confident—on the inside when they can point to things they have done well on the outside. 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.

19. Our personalities change more during the twentysomething years than at any time before or after. In our twenties, positive personality changes come from what researchers call “getting along and getting ahead.” Being a cooperative colleague or a successful partner is what drives personality change.

20. Steady relationships reduce social anxiety and depression as they help us feel less lonely and give us the opportunity to practice our interpersonal skills.

21. Being single while you’re young may be glorified in media, but staying single across the twenties does not typically feel good.

22. There is a biological clock that ticks inside for both men and women and fertility. As people age, it becomes harder and/or more costly to become pregnant.

23. We now know that the brain has difficulty keeping time across long, unpunctuated intervals. We condense unmarked time. The days and years pass, and we say, “Where did the time go?”

24. People of all ages and walks of life discount the future, favoring the rewards of today over the rewards of tomorrow. This “time inconsistency” is a human tendency, not just exclusive to twentysomethings. This underpins addiction, procrastination, health, oil consumption, and saving for retirement.

25. The future isn’t written in the stars. There are no guarantees. So claim your adulthood. Be intentional. Get to work. Don’t be defined by what you didn’t know or didn’t do. You are deciding your life right now.


Relatable stories

Meg teaches through real stories of clients she has interacted with. The twentysomething clients vary and are relatable in one way or another. Being able to relate to these individuals is helpful because you’ll realize you have similar thoughts, backgrounds, problems, aspirations, etc.

With that, you’ll be reassured that you are not alone in what you are going through. You can read about others, see how they overcame their situation, and use that to help you in your own situation.

Author has countless hours of practice

It would be easy for any person past their twenties to write a book giving advice to twentysomethings. The Defining Decade is a lot more than that.

Meg may touch on her own twenties experience a few times, but the bulk of the content comes from her interactions with twentysomethings.

After countless hours of practicing as a psychologist, she started to see common denominators between everyone. You aren’t learning from one person. You end up learning from the cumulative group that Meg Jay has worked with.

This can give you confidence that the chapters in the book are written on the most pressing issues for twentysomethings.

Covers work, love, and the brain and body

I enjoyed the comprehensive structure of the book. There are three sections that cover 1) work 2) love and 3) the brain and body. Optimizing all three is important in living a well-rounded life.

I was able to relate the most to the chapters in the work section and found the chapters in the brain and body section most insightful.


No more wasted time

I’m in my mid-twenties now and can tell you that it’s easy to let your twenties waste away. You believe in “YOLO” and that you should live it up while you’re young.

I fully agree with this but within reason. There is a balance between living your life and preparing for the rest of your life.

Take action during a pivotal point in your life

View your twenties as a trampoline to launch you into the rest of your life.

In your twenties, your personality will change the most it ever will. Your wage growth will accelerate the most it ever will. Your brain is still able to learn things quickly and will finish developing in your mid twenties.

Take advantage of this time by doing all you can. Set your career, finances, health, and love life on the right path. Experience life and build up identity capital.

Minimize regrets in your 30s and 40s

This book will help you stop wasting time so you aren’t regretful in your thirties and forties.

Meg shares many stories and quotes from regretful thirtysomethings and fortysomethings. It’s sad to read about and acts as a wake up call to the reader. Learn from their mistakes and you won’t have the same regrets.


1. Cultivate and maintain awareness of how important your twenties are. 30 is not the new 20.

2. Take the time to explore and make commitments. Get out of your comfort zone. Take work leaps or a wider range of jobs. You will build up identity capital.

3. Look for opportunities outside of your inner circle. Without overlapping connections, information and opportunity are more easily spread through weak ties.

4. Change your mindset. Instead of being bitter that your first job is not your dream job, see the lessons you can learn from the job. Use it to develop so you can work your way towards your dream job and career.

5. When interviewing, try to tell a story. Interviewers remember the candidates that made them feel something. A good story goes further in the twentysomething years than any other time in life.

6. Monitor the stories you tell yourself. The stories we tell ourselves become pillars of our identity.

7. Take advantage of your brain’s plasticity in your 20s. While you can still learn in your 30s or 40s, it isn’t as easy.

8. Develop a growth mindset, which is when people believe they can change as a result of their own actions. They believe success is something to be achieved and not something innate.

9. It’s easy to become stressed at the start of your career. Realize you won’t be an expert from the start. You’ll likely need to put in about 10,000 hours of work to become a master.

10. Treat your future self as good or better than you treat your current self. Don’t fall into the clichés of “YOLO” and “Have fun while you can.”


The Defining Decade can be found on Amazon at this link here if you are interested in reading.

About Post Author

Brandon Hill

I'm Brandon Hill with Bizness Professionals. We serve content to help young professionals develop personally, professionally, and financially. Well-rounded improvement is a theme we live by. As such, this website will cover a variety of topics aimed to help you have a successful life and career.

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