An Aesop Fable;

A man who had been bitten by a dog went about in quest of someone who might heal him. A friend, meeting him and learning what he wanted, said, “If you would be cured, take a piece of bread, and dip it in the blood from your wound, and go and give it to the dog that bit you.”  The man who had been bitten laughed at this advice and said, “Why? If I should do so, it would be as if I should beg every dog in the town to bite me.”

Benefits bestowed upon the evil-disposed increase their means of inuring you.