Book Review: The Defining Decade by Meg Jay

The Defining Decade
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Author: Meg Jay
Published: Apr 2012

Goodreads: 4.1/5
Barner&Noble: 4.6/5
Amazon: 4.7/5
(Jan 2020)

I bought this book when I was 20. At that time, I fell that this is a good read, however, not really beneficial for me, as I believed I was more disciplined than the people mentioned as examples in the book.

5 years later, when this book is still popular (which means many find it useful) and when I realized my thoughts have changed much in this half a decade, I decided to re-read it to see if there is anything good that I can consume. The experience this time is different. Despise my scrutiny style of work (that often makes me indecisive, I admit), I still almost miss some milestones-of-life that are mentioned in this book.

I would recommend reading The Defining Decade if any of the below applies to you:

  • If you are between 18 to 35 years old, a read each couple of years is valuable. Make this a checklist, a reminder or a drafted plan of your coming life.
  • If you feel you missed, or about to miss an important milestone in your life because you were too careless and irresponsible in your 20s.
  • if some of your loved ones suffer from the above grief and you want to give them advice.

The book is structured around 3 parts: work, love, the brain and the body.

In the modern world, many young people tend to postpone their stages of life, including their work and marriage, to enjoy their 20s. This, in Meg Jay’s point of view, creates a detrimental effect on their incoming ages. She disagrees with the statement “30s is the new 20s” which indicates that in this generation, humans are allowed to start everything that humans in the old generation started in their 20s, in the 30s. Those include getting married, giving birth to children, finding a job and planning for the future. She argues that youngsters should stop thoughtlessly enjoying their lives in their 20s, as the 20s play a very big role in one’s duration (80% of important events occur before the age of 35).


The problems of young people that are listed in this chapter are:

  • Some are not so sure who they are, or which careers they are pursuing. As introduced in the subsection about Identity Capital, they tend to have their days passed with their worthless part-time jobs. These jobs give them a feeling of working and earning, while they are actually unfavorable to those people’s career paths. As time passed, these people will be left further and further behind by the fellows who spend their time on something fruitful for their future.
  • Some, especially those who seem to have many options, are reluctant to select one. They postpone their selection like forever until they recognize that much time has passed and they are left along when the others have gone too far ahead. As an example, Sheena Iyengar, a researcher at Stanford, do an experiment involving advertising marmalade. It shows that customers who are introduced to 24 types of marmalade rarely buy (only 3%) while customers who see only 6 types of marmalade have a much higher rate of buying (30%).
  • Some underestimate the weak ties (the not-so-intimate relationships). According to research conducted by Granovetter (a professor at Stanford University), over 75% of work comes from someone we sometimes or rarely meet. People often have a tendency to communicate and spend time with a fixed group of close friends. Although that is not something we should complain about, it does have a bad side if we don’t make efforts to expand our networks. Close friends or close relatives often have a lot in common with us, their knowledge/experience/vision is to some extent similar to ours, which in turn results in the lesser new knowledge/experience/vision we can learn from. The weak ties, on the other hand, are much more different, thus we can expect to inherit more from them.
  • Facebook, the social network which is often claimed to help keep connections with old friends and relatives, is actually used as an exhibition of our lives. Furthermore, people tend to display only the good parts of one’s life but believe that he/she is the only one doing so. This makes people depressed thinking others are happier than themselves.
  • Some dislike predictable lives, they hate it when their future is defined as normal, often by having a boring and repetitive job. They want their lives to be customizable and be different from any other. They do not advance when they could not see anything novel, however, the problem is, if only they push themselves forwards do they find the novel and unique work they wished for.


  • Singles of the new generation have a tendency to postpone their marriage to older ages in order for themselves to be more mature and thus, be able to choose the one more wisely. However, the ratio of divorce is still around 40% despite the fact that people are having their marriage 5 years later than the previous generation. Research shows that the rate of divorce decreases as our ages come to 25 years old, but after this time, the age of marriage does not affect the divorce rate anymore.
  • Some are not really serious when choosing the right partner. Research on female participants reveals that the major part of them considers their bad marriages is what they regret the most in their whole life.
  • People, especially the ones who are not so happy with their parents, usually uphold the statement “we can’t choose our family but we can choose our friends”. However, this is not the case when you are marrying. You can choose your small family (by choosing your spouse) and even choose the family of your spouse. It is NOT that because your family is not perfect then you do not have the right to expect a good family from your companion.
  • Cohabitation is becoming more popular. People (lovers) cohabitate to see if they are really suitable before deciding their wedding. About half of the 20s years olds live with their partner at least once before getting married. Nevertheless, if you are living with each other but don’t function it the right way (that is, your simulation is different from the real), you are not getting the result you want. Cohabitation even has a risk of making couples too attached to each other (having the same friends, shared furniture, cheaper housing, etc), which in turn leads them to marriage (even though they are not so sure) and then break up afterward. Not being for or against the cohabitation trend, the author just gives a warning of the bad effects cohabitation may bring.
  • Due to some reasons, some people have an immoderate use of dating. They date without thinking or considering what consequences may follow. They are not just wasting their time, but also crafting an unreasonable and worse picture of themselves, in their own eyes and others’ eyes. Being serious about their relationship is what they should be considering.
  • Some are not focusing on the right points when evaluating their partners. In her book, Meg Jay takes an example of two couples: Eli and his girlfriend, together with Matt and Courtney. In the case of Eli, since both he and his partner are of collaborative type, they accept their relationship for a long time without realizing that it can not last long as they are not actually good matches for each other. This is in the opposite for Courtney, while she cares about the miniature detail too much and does not recognize the good things about Matt.

The brain and the body

  • In the first 18 months after birth, the brain goes through the first big progression, creating more neurons than it can actually utilize. The second (and also the last) big progression starts on the teenage and ends in the 20s. Furthermore, what we learn in this second phase is not bounded by basic skills like vocabulary or socks or shoes. This time, it is for preparing for mature life. Being similar to a child who can learn any language he is surrounded by, the people in their 20s are most suitable for learning and working to prepare for their whole remaining future, biologically. 20s is the age of being busy, not relaxed.
  • Our brains work best when they perceive weird things. In our 20s, we have to have many transformations in our lives, many new (and weird) things will happen to us, making this the age when our brains are most effective, so it is rational to have the brains work on the beneficial thoughts, skills, and knowledge. In older ages, we are not that sensitive anymore, a lower rate of learning is following this defining decade. The author also doesn’t forget to remind readers that if you are at the age of 20s, you are supposed to be sensitive to changes, everyone is, so, knowing that and don’t get despaired when facing difficulties, try to make it through when crisis come by.
  • Research shows that people don’t change much after they reach 30. Personality changes in the age of 20s more than any other period of life. Hence, this is the best chance for us to form our ideal characteristics, to be who we really want to be for the rest of our time.
  • Those who are in their 20s and have even a little bit of success or financial position are usually more confident and positive.
  • Having a target makes us happier. Apart from jobs, a commitment also improves happiness.
  • In a questionnaire, 52% of the 20-something-year-olds have their most important goal to be a good parent, while this number is only 30% for having a good marriage and 15% for a good-salary job. While most claimed their priority for their kids, their actions do not lead them to their target. Nowadays, people who are at least 35 are giving birth more than teenagers. 1/3 of the first-children were born when their moms reached 35. These facts of late-coming babies are making worries since our biological bodies are not programmed for giving birth at older ages. Female fertility reduced to 1/2 at 30, 1/4 at 35 and 1/8 at 40. When you are young, you have about 20-25% of being conceived in each period, this number reduces to 5% in 40, 3% in 41 and 2% in 42. Furthermore, 1/4 are miscarried at 35, 1/2 at 40.

My final thoughts

I like the way Meg Jay tells the story with examples from her own experience as a clinical psychologist. This book seems to be most suitable for the female US or European youngsters, however, although being an Asian boy, I still see myself being attracted to.

The book: The Defining Decade: Why Your Twenties Matter–And How to Make the Most of Them Now

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