When you deposit money, it's no longer your money. You've now lent the money to the bank. That bank may or may not be worthy of your trust, and there are likely

When you deposit money, it's no longer your money. You've now lent the money to the bank. That bank may or may not be worthy of your trust, and there are likely rafts of laws protecting you. But ultimately it's a loan to the bank. All you own is an acknowledgement from this institution that they owe you $x. On the other hand, if you buy shares in the bank, you now own a chunk of it. Of course this isn't a feasible way to keep your day-to-day cash; we all need checking & credit accounts. But anything above the minimum is a risk, and a lost opportunity from investing returns you could've gotten from shares, bonds, or even the money market. For that minimum expense float we all need to have, cash under the mattress is not that terrible of an idea, assuming you live in a safe place. Something to keep in mind!