Lesson 2 of 8
Diversification, explained simply
6 min read
Diversification is the only thing in investing that reliably reduces risk without reducing expected return in equal measure. It is as close to free as finance gets.
What it actually requires
Owning ten technology shares is not diversification - they rise and fall together. Real diversification means holding assets with low correlation: different companies, different industries, different countries, and different asset classes such as bonds alongside shares.
The purpose is not to maximise returns. It is to ensure that no single company, sector or country failing can be decisive for your outcome.
Why index funds dominate the conversation
A broad index fund buys an entire market in proportion, so a single low-cost holding can provide thousands of companies across dozens of countries. That is why they are the default building block for most long-term investors: instant breadth, low charges, no reliance on anyone's stock-picking skill.
Home bias
Most people hold far more of their own country's market than its share of the world economy justifies - home bias. It feels safer because the names are familiar. In reality it concentrates your investments in the same economy that already pays your salary and holds your property.
Concentration risks that hide in plain sight
- Large holdings of your employer's shares: your income and your investments then depend on one company.
- A single property representing most of your net worth.
- A crypto holding large enough that its drawdown would change your life.
Rebalancing
Over time, whatever performed best grows into an outsized share of your portfolio and quietly increases your risk. Rebalancing once a year - trimming winners, topping up laggards - restores the mix you chose deliberately. Watch out for costs and any tax consequences when you do it.
Key terms
- Diversification
- Spreading money across many holdings so no single failure is decisive.
- Correlation
- How closely two investments move together. Low correlation improves diversification.
- Index fund
- A fund that holds an entire market in proportion, at low cost, rather than picking stocks.
- Home bias
- Over-weighting your own country's market simply because it is familiar.
Quick check
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Homework
0/3 doneThree small jobs. They take minutes and they're what makes the lesson stick.
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Make it personal
In two sentences, write what "Diversification, explained simply" changes about how you handle your money this month.
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Teach it back
Explain the main idea of this lesson in plain English, as if to a friend. Write the explanation you would give.
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