It would be a great mistake to suppose that it is sufficient not to become personal yourself. For by showing a man quite quietly that he is wrong, and that what he says and thinks is incorrect — a process which occurs in every dialectical victory — you embitter him more than if you used some rude or insulting expression. Why is this? Because, as Hobbes observes, all mental pleasure consists in being able to compare oneself with others to one’s own advantage. — Nothing is of greater moment to a man than the gratification of his vanity, and no wound is more painful than that which is inflicted on it. Hence such phrases as “Death before dishonour,” and so on.
Arthur Schopenhauer, The Art of Always Being Right
vanity