Why do people say your like a bad penny keep returning?

The phrase "like a bad penny, you keep returning" suggests that someone or something undesirable keeps reappearing despite attempts to be rid of it. It implies a sense of frustration, as if the person or situation is persistent and unwelcome, much like a worthless coin that keeps turning up. This expression often highlights the inevitability of dealing with certain issues or people, no matter how much one tries to avoid them.