Suppose I am walking to school. A boy named Johnny who is my friend, walks up to me, smiles and asks me:
Hey, Sam! Do you know when class starts?
I reply to him:
No, sorry Johnny. I left my timetable at home like you did.
Johnny's facial expression then transforms into one marked by a simultaneous disdain and anger towards me, because he only wanted to use me as an agent to give him information, for which I at the present could not.
The natural person, in this situation, would not consider Johnny a good friend anymore because a good friend is not someone who values you based on your ability to augment his daily life. However, In this hypothetical scenario, I would feel sympathetic for Johnny, because what if, hypothetically, Johnny was as good if not as good as me but grew up in certain conditions that fostered such a parochial outlook and hence, for factors beyond his control, is the person he is today. Then, in that case, I feel morally obliged to treat him even more kinder. Simultaneously, I am reinforcing his behaviour because I am showing him that it is okay to treat people like this.
Conversely, If I exhibit madness at him, and show clear disapproval at his behaviour, I am simultaneously telling him it is wrong whilst making his life harder because I now am a source of negativity in his life. In this sense, I reinforce the negativity in his life and may potentially contributing to a more negative individual.
In the first option, it is not sensible to treat people better for treating you bad, and this is what I am doing. On the second option, it is not sensible to treat people negatively because they treated you negatively too.