It's maybe because they are looking for love more than for money. If you let it go, they will have a right to believe that you think you owed it to them for all they've done for you, or you like them a lot and wish them well. They want to have the feeling that they have a true friend in this world, almost like a brother or sister who loves them. They are craving acknowledgment from others. When days and weeks go by without your asking for the money back, this reinforces their fantasy that you want to be their friend. It makes them feel secure. Actually, I think these same borrowers, if they are righteous people, will pay you back as soon as they get a financial breakthrough. However, you know as well as I that if they are vicious users, criminals of any kind, substance abusers, forgetful, irresponsible, insane, or desperate people, you probably won't ever get money paid back to you. That, I think, is the psychology behind what puzzles you. One of my aunties had a theory that most people fall into one or the other category: either they are givers or they are takers. There's an old expression, it's better to give than receive, but one exception to that maxim is that no one likes to get taken. Still, if you are up against an impossible type of person who refuses to pay you back, there isn't much you can do. If it's major, and is the kind of thing the courts should know about, you could go to small claims, or hire a lawyer, but I have the feeling your situation probably is a personal thing. I am sorry for you. The same has happened to me more than once, including times when I thought the person was honorable but they were not, and times when I just let things go because the person was a friend or a family member.