Revenge and Reciprocity

Poor Donald is quoted as saying that all he knows is revenge. This leads me to wonder if revenge is merely the obverse of reciprocity. If someone only experiences injury, what does he give back but revenge? Reciprocal negativity. How does perverse perception come about?

That he threw stones at a baby in a playpen and yelled “Make the baby cry,” is just too monstrous. He must have been damaged at birth.