if you only said I'm going to hide some amount of my money under my mattress and I'm going to put the rest in equities, the amount I'm going to put in equities, I'm going to determine by my risk tolerance and capacity, right? And let's say, okay, that means 50% of my money is in equities and I'm going to put 50% under my mattress.

Then the question is, well, what else can you do with it? And what you find is like, if you assign some amount of diversification and actually negative correlation to the bonds, that means you may actually be able to put 55 or 60% of your portfolio in equities and the rest in bonds.

Because if equity moved down and bonds move up, then your total portfolio drop is going to be lower than if you just had 50% in equities and the rest under your mattress. And instead of putting it on the mattress, you could have it in cash or in treasury bills, for example.