Margen
Harry Markowitz won the Nobel Prize in Economics in 1990 for proving mathematically something that sounds like a proverb: combining investments that don't move together lowers your risk without giving up the same expected return. That's why diversification is called 'the only free lunch' in investing — one of the very few upgrades you don't have to pay for.
The logic is simple: if all your money depends on one thing, so does your future. Eight baskets with one egg each survive stumbles that one basket with eight eggs won't.
And the human detail: asked how he invested his own retirement money, Markowitz admitted he split it half and half between stocks and bonds — simply to minimise his future regret.
Even the father of portfolio theory invests so he can sleep at night. That, too, is a return.