The most common portfolio mistake isn't bad stock selection or wrong market timing. It's concentration — having too much money in too few things. It's so common because concentration often looks like conviction, and in bull markets it looks like brilliance. In bear markets, it looks like exactly what it is.
Investors typically focus on stock concentration (too much in one company) but forget there are two other dimensions:
Every country's investors systematically overweight their domestic market — called home bias. It feels safer. You know the companies. The currency matches your spending. But the UK is 4% of global market cap. Overweighting it to 40–50% of a portfolio is a massive concentrated bet on one economy, one political environment, and one currency — often unconscious.
The fix — and it's simple: a single global equity index ETF (MSCI World or FTSE All-World) gives you exposure to ~1,500 companies across 23–50 countries, weighted by market cap. One fund, no concentration decisions required. It sounds boring because it is. It's also the allocation that most active stock-pickers fail to beat over 20 years. Concentration is a bet. Diversification is the default. If you're going to deviate from the default, be very clear about why.
Answer questions on concentration risk, earn XP, and challenge your mates to a stock duel.
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