"Even if we are right and the other person is definitely wrong, we only destroy ego by causing someone to lose face. The legendary French aviation pioneer and author Anotoine de Saint-Exupery wrote: "I have no right to say or do anything that diminishes a man in his own eyes. What matters is not what I think of him, but what he thinks of himself. Hurting a man in his dignity is a crime."
from: How to Win Friends and Influence People by Dale Carnegie
(sometimes we teach what we need to learn~)