I could rent a car to a customer at a daily rate. At the end of the day I get the car back plus a rental fee. That's the same as earning interest on an investment. Those revenues would allow me to buy a new car when the old one breaks down, pay for my own expenses, and perhaps even expand my business.

If I didn't charge a fee, then the car would gradually lose value, I would not be able to cover my expenses nor replace the car with a new one when it wore out. However, the person who borrowed it got use of it, but didn't lose anything. This represents a transfer of wealth. When applied to the straight cash banking & investment industry, someone is losing money. It would be considered ingenius if it weren't criminally-motivated.