Diversification.

In plain English

Diversification means owning a variety of investments, different companies, different industries, sometimes different countries and asset types, so that one bad outcome doesn't sink everything. It's the financial version of 'don't put all your eggs in one basket.' The cleanest way to be diversified is to own broad index funds, which spread money across hundreds or thousands of holdings automatically.

01Why it matters

Concentrated bets can have huge upside but also catastrophic downside. Companies you've never heard of go bankrupt every year; even famous companies lose 80%+ of their value sometimes. Diversification doesn't make your returns better in any single year, it makes them more predictable across all years, and it prevents the one bad outcome that wipes you out.

02The math, step by step

If you put $100,000 into the stock of one company and that company goes bankrupt, you lose $100,000. If you put the same $100,000 into a total-stock-market index fund (which holds about 4,000 companies), even if 50 of those companies go bankrupt that year, your loss from those 50 is tiny, typically a fraction of a percent of the total. The remaining 3,950 companies do their normal thing.

Illustrative example. The amounts here are hypothetical, chosen to show how the math works, not real quoted rates or figures.

03What this is NOT