Build your own portfolio
This is my understanding, for education. Not personal financial advice.
Diversification protects wealth. Concentration builds it. Sizing keeps you alive.
Conventional advice says diversify. Own everything. I think that advice is built for people who are already rich and want to stay rich. If you're starting with a small account, owning everything mostly guarantees average.
What diversification really does
Diversification spreads money across many investments so no single one can hurt you much. That lowers the swings. It also lowers the chance that any one big winner changes your life. Remember from Chapter 4: about 4% of stocks created all the net gains since 1926. An index owns those winners, but in tiny slices, alongside everything else.
For someone with $5 million, protecting it makes sense. For someone with $5,000, a well-researched, concentrated bet on a few great businesses is how real wealth gets built. Most rich people got there through one company, not a balanced portfolio.
The catch: concentration is a skill. Most professional stock pickers trail the index over 10+ years (SPIVA). That's why Chapter 5 comes first, and why you should measure yourself honestly against the index every year.
The math that makes sizing matter
Swings eat compound growth. This is called volatility drag:
| Year 1 | Year 2 | Result on $10,000 |
|---|---|---|
| +50% | −50% | $7,500 (down 25%) |
| +25% | −25% | $9,375 (down 6%) |
| +10% | +10% | $12,100 (up 21%) |
The average return in the first row is 0%, but you lost money. And losses need bigger gains to recover:
| Drop | Gain needed to get back |
|---|---|
| −20% | +25% |
| −40% | +67% |
| −50% | +100% |
| −66% | +194% |
Kelly: even a sure edge has a right size
In 1956, John Kelly worked out how much of your bankroll to bet when you have an edge. The key insight: the bet that grows wealth fastest is never "everything." Betting more than the Kelly amount raises risk and actually lowers long-term growth, and betting 100% means one bad outcome ends the game. Traders often use half of Kelly or less, because their edge estimate is uncertain.
You don't need the formula. You need the lesson: the size of the bet matters as much as being right.
A concentrated, survivable portfolio
Here's how I'd think about it (adapt to your own life): 1. Cash buffer first. 3–6 months of expenses, plus any money needed within a few years. This is what lets you never sell in a crash. 2. Core conviction names. 3–5 businesses you've researched with the Chapter 5 checklist. Bigger positions in the ones you understand best. 3. Size for the drop. Before you buy, ask: if this falls 60%, can I hold it, and keep buying? If not, it's too big. 4. Keep adding. Monthly buying (Chapter 7) turns drops into discounts. 5. Write a thesis. One paragraph per stock: why you own it, what would prove you wrong. Reread it when it drops. 6. Score yourself. Compare to the S&P 500 once a year. If you trail for years, that's information.
Where to hold it
Tax-advantaged accounts (Roth IRA, 401(k) with an employer match) let gains compound without tax drag. The Library page on retirement accounts keeps the 2026 limits.
No leverage
Concentration plus margin is how people get wiped out. Brokers can sell your shares at the bottom to cover a margin loan. Concentrate with your own money only.
Concentrate on purpose, size it so a 60% drop can't knock you out, and keep adding.
Sources
- Kelly, J. L. (1956), A New Interpretation of Information Rate, Bell System Technical Journal: https://doi.org/10.1002/j.1538-7305.1956.tb03809.x
- SPIVA US scorecard: https://www.spglobal.com/spdji/en/spiva/article/spiva-us/
- Bessembinder (2018): https://wpcarey.asu.edu/sites/g/files/litvpz246/files/2021-10/do-stocks-outperform-treasury-bills.pdf
- Investor.gov on margin: https://www.investor.gov/introduction-investing/investing-basics/glossary/margin-account
