Diversification: why you shouldn't put everything in one place
Diversifying is spreading your money across different assets so a single blow doesn't sink your portfolio. It's one of the few "free lunches" in finance: done well, it reduces risk without necessarily giving up returns. But many people think they diversify when they actually don't.
Why it works
The idea is simple: if you have all your money in one stock and that company collapses, you lose almost everything. If you spread it across many, one disaster is cushioned by the rest. You don't put all your eggs in one basket. The key is that the different assets don't rise and fall exactly together: when some fall, others hold or rise, and the whole is more stable.
Real diversification: assets that don't move the same
Here's the nuance almost nobody gets: diversifying isn't "having lots of things", it's having things that react differently to what happens. Holding 20 tech stocks isn't diversifying: if the tech sector falls, they all fall together. Real diversification is combining assets that respond differently to the same circumstances.
The typical mistake: false diversification
Many people have ten positions and think they're diversified, but if they're all the same type (same sector, same region, same asset class), they're actually concentration in disguise. When the blow that hits that group arrives, everything falls together. Having many correlated positions gives a false sense of safety the market breaks at the worst moment.
The other extreme: over-diversifying
You can also overdo it. Spreading money across fifty different things dilutes your best ideas so much that being right doesn't matter: the impact is minimal, and it's impossible to follow. Diversification has a sweet spot: enough to protect you from a concentrated disaster, without so much dispersion that your portfolio is an expensive replica of the whole market.
Where to start
Look at your portfolio and ask an honest question: if something bad happened in a specific sector or region, how much of my money would be affected at once? If the answer is "almost all", you're not diversified no matter how many positions you have. ETFs, by their nature, are a simple way to diversify in one go, which is why they're so popular with beginners.