It can be a business actually, you can double up the payment if ever they borrow to you. For example, in bitcoin, someone borrowed it to you and suddenly the value of bitcoin grows up. They will now need to pay you higher since the value grew up all of a sudden. You should not be so generous with it though even if that's the case because some of them may run and hide to you if ever the value grows to large. Make sure always that those whom you've given the opportunity to borrow is trustworthy enough and not just a normal and complete stranger.