Anyone with collateral can go into debt at 3%(ish) interest. I've never heard of anyone getting a sizable loan for longer than overnight at that rate without collateral. If there is a counterexample please share it. And if a person defaults on a collateralized debt, well, they lose, and usually badly. Margin calls are one of the nastier examples, but foreclosures also come to mind. Even a safe investment like US Treasury bonds can trigger a margin call if, for example, interest rates rise and reduce the market value of the bond enough to fall below margin requirements.