At certain times in life, we have borrowed money from someone. When a person lends money to somebody, they have faith in that person to promptly return the money as soon as possible, though this is rarely the case. The reality is, most people do not give back the money, and this is how loan sharks and credit card companies make money from people by charging late fees and interest. These people only return the money because the interest legally starts piling up.
The person who loaned the money will usually get very angry, and we know what people will do when it comes to money. If you owe someone potentially dangerous money, it is usually a good idea to promptly return it.