Needs...survival as said above. I don't remember who wrote about this concept, but people have a need to see themselves a certain way--the ideal. Which was developed to survive the parents...someone might have had to be 'good' to avoid abandonment and rejection from parents.

So later on, threats to ego surface when something/someone is misaligned with how the self is viewed. ie- he sees himself as a good person, but the T scorned him. In self psychology (I think), the size of the gap between how one sees himself and how seen by another through words or actions corresponds with degree of threat to the ego.

Maybe it hurts because the person relives the feelings of a lifetime of rejection or abandonment?