Why do people give specific warnings about certain relationships, like avoiding certain names, and is there really any validity to that advice?

Why do some people with disabilities take advantage of those who are kind enough to help them?
Why am I so in love with this girl that I would let her sleep with another guy just so she can stay with me?
Do you think people who repeatedly answer your questions, in some sense, are meta-ethically ''obligated'' to follow you back?
Have you ever unintentionally stunned someone with a response that wiped their smirk right off? What was the situation and your reaction?