Book Cover
The Defining Decade

★ ★

TL;DR: Mostly stories. Entertaining read, not much actionable. Good reminders to get my ass into gear.


  • 80% of life’s most significant events happen before 35


  • 20-somethings are like airplanes. A small course change right after takeoff wlil make a huge difference. A small course change close to destination won’t matter much
  • Identity capital: collection of personal assets. Repertoire of individual resources we assemble over time. Investments in ourselves, things we do well enough that they become part of who we are
    • Resume pieces and personal pieces
    • Currency for purchasing jobs, relationships, other things we want
  • You can’t think your way through life
  • Urbanization has killed weak ties
    • “Strength of Weak Ties” (Granovetter)
      • 75% of new jobs come from weak ties
    • Because they’re not just figures in an already ingrown cluster, weak ties give us access to something fresh
  • Ben Franklin effect: if someone does you a favor, they’re more likely to think they like you
    • Behaviors shape attitudes
  • Unthought known: we know about ourselves but we forget (dreams, truths, acknowledgements)


  • Roulette
  • Marrying later protects against divorce until about age 25
  • People feel an “Age Thirty Deadline”
  • Best time to work on marriage is before you have one
  • YAVIS: young, attractive, verbal, intelligent, successful – give advantages but makes it hard when you want to seek help
  • You are picking a family when you get into relationships
  • The cohabitation effect is that couples who live together before marriage are more likely to divorce than couples who do not
    • “Sliding, not deciding”. Things get fuzzy
  • Do a Big Five test with each other
  • Be picky about stuff that matters in 20 years, not about everyday discrepancies

The Brain and the Body

  • Frontal lobe development in adolescence and 20s. Most neuroplastic you will ever be again
  • If you don’t feel anxious, you’re either overconfident or underemployed
  • Don’t take things personally
  • Confidence comes from mastery experiences
  • Most personality change happens in 20s
  • Fertility risks are real :(
    • Per-cycle odds of conception are 20-25% up to age 35
    • Sharp drop to 5% at 40
    • Miscarriages: 1/4 of after-35 pregnancies and 1/2 of after-40 pregnancies
  • Present bias: people discount the future all the time