Another way to understand banking is that they borrow interest free credit and use it to buy assets like bonds and loan contracts. This credit creation amount is leverage based on their investor bank capital, not customer deposits. So when they find an asset to purchase they merely record the credit creation as a loan they must pay back and this is why the majority of their purchases are as secure as possible, usually backed by an asset itself, like a house, the car, biz assets, or the faith of the government. They are limited to these secure assets otherwise they would take too many risks and suffer insolvency more often due to leverage of up to 30x (BIS 3% capital adequacy ratios)