Being a DeFi lending protocol, Aave has removed intermediaries from financial processes, such as asset trading, taking out loans, etc. Hence why when users lend, they earn interest. When they borrow, they have to pay interest. However, Aave requires over-collateralization. Therefore, if you want to take out a $100 loan, you would have to put up more than the initial amount you are planning to borrow. In the event of a shortfall event, the protocol can take your collateral to cover the costs of the loan.