"Don't put all your eggs in one basket" is probably the most repeated piece of financial advice in history, and it still holds up because it accurately describes one of the most solid principles in modern portfolio theory: diversification.
What diversifying means
Diversifying means spreading your capital across different assets, sectors, regions, or investment classes, instead of concentrating it all in a single asset or issuer. The core idea is that if one particular asset performs badly, the impact on your overall wealth is cushioned by how the others perform.
Why it reduces risk without necessarily reducing returns
This is the point that tends to surprise people new to portfolio theory: diversifying properly can reduce your portfolio's risk without proportionally sacrificing expected returns. This happens because part of each individual asset's risk is specific to that asset (diversifiable risk), and it can be reduced by combining it with other assets that don't move exactly the same way, without that meaning you have to give up the average expected return of the combined portfolio.
What diversification can't eliminate
There's a limit: so-called market risk (or systematic risk), which affects virtually all assets within the same class at the same time (for example, a global financial crisis hitting most of the world's stock markets simultaneously), can't be eliminated just by diversifying within that same asset class. Reducing that risk requires diversifying across different asset classes too (equities, fixed income, real estate, cash), not just among individual securities within the same class.
Practical ways to diversify without managing hundreds of assets
Building a portfolio with dozens or hundreds of individual assets by hand isn't realistic for most individual savers. Index funds and ETFs that track broad indices are precisely a way to achieve very wide diversification (sometimes hundreds or thousands of underlying securities) with a single transaction, and generally with lower management fees compared to active management.
The "false diversification" mistake
A common mistake is thinking you're diversified just because you hold several different products, when in reality they're all highly correlated with each other (for example, several funds that each invest mainly in the same big tech companies). Holding several products isn't the same as being genuinely diversified if their performance tends to move in the same direction in response to the same market events.
Diversification doesn't replace planning
Diversifying reduces specific risk, but it doesn't eliminate overall market risk, nor does it replace sound financial planning suited to your time horizon and your personal risk tolerance. No diversification strategy guarantees positive returns in the short term.
Simulate different return scenarios
Our compound interest calculator lets you compare how your capital would grow under different assumed average return scenarios, useful for weighing the long-term effect of a more or less diversified portfolio.