Diversification
Diversification is spreading capital across uncorrelated assets to reduce risk without proportionally reducing return --- the only free lunch in finance.
What is it?
Harry Markowitz demonstrated in 1952 that combining assets which do not move in lockstep reduces portfolio risk below the risk of any individual asset.1 This is not averaging --- it is a mathematical property of combining independent uncertainties.
If you hold one stock, a bad earnings report can cut your portfolio by 30%. If you hold 500 stocks across different sectors, a single bad report barely registers. The specific risk of each company washes out. What remains is the systematic risk of the market as a whole --- which you are compensated for through the risk-and-return premium.
The principle extends across asset classes. Stocks and bonds often move in opposite directions. Adding bonds to a stock portfolio reduces volatility more than it reduces return --- a genuine improvement in the risk-return trade-off.
In plain terms
Don’t put all your eggs in one basket. But the deeper insight is why: a basket of 30 uncorrelated eggs is safer than 30 eggs in one basket, even if each individual egg is just as fragile.
How does it work?
What diversification eliminates
- Company risk (one company fails) --- eliminated by holding many companies
- Sector risk (one industry declines) --- eliminated by holding multiple sectors
- Country risk (one economy struggles) --- eliminated by investing globally
- Asset class risk (one class underperforms) --- reduced by holding multiple classes
What remains: market risk --- the risk that all assets decline simultaneously (global recession, systemic crisis). This cannot be diversified away. It is the risk you accept in exchange for the equity premium.
Practical diversification
The simplest diversified portfolio is a global stock index fund (thousands of companies across all sectors and countries) plus a bond fund. Two funds. Instant diversification. This is why index investing has become the default recommendation from financial economists: it provides maximum diversification at minimum cost.2
For someone in Switzerland, a practical allocation might be:
- Global equity index (MSCI World or FTSE All-World) --- broad diversification
- Swiss equity index (SMI/SPI) --- home bias for currency matching
- Bond allocation --- Swiss government or investment-grade corporate bonds
- 3a invested --- often mirrors the above within the pension wrapper
The concentration trade-off
Diversification reduces risk but also caps upside. Holding 500 stocks means you will never earn the return of the single best stock. For investors, this trade-off is almost always worth it. For entrepreneurs, it is reversed --- concentrating effort on one venture creates the possibility of outsized returns (but also outsized loss).
The resolution: diversify your investments, concentrate your effort. Your financial portfolio should be broadly diversified. Your career and venture portfolio can be concentrated on your highest-conviction bet.
Check your understanding
Five questions (click to expand)
- Explain why a portfolio of 30 uncorrelated assets is less risky than any single asset, even though each asset is equally risky.
- Distinguish between risks that diversification eliminates and risks it does not.
- Design a simple diversified portfolio using two or three funds. What does each component contribute?
- Connect diversification to the principle “diversify your investments, concentrate your effort.” Why does this make sense?
- Evaluate this claim: “If you really believe in a company, you should go all in.” What does diversification theory say?
Where this concept fits
Where this concept fits
graph TD RR[Risk and Return] --> DV[Diversification] AC[Asset Class] --> DV DV --> PC[Portfolio Construction] style DV fill:#4a9ede,color:#fff