doing the same thing over and over again and expecting different results.
Part of being human is being a creature of habit... this includes doing things that make us feel comfortable, even if it means doing something that isn't very smart. And some of it has to do with our hard-wired preferences... after all, some people prefer vanilla, while others like chocolate. Go fig.
My ex-fiancee's father told me to "go out and go meet a nice girl with not mental illness." That's a direct quote.