Samuel Johnson says that those who constantly engage in self-deprecation are really guilty of “oblique praise.” It has “all the invidiousness of self-praise, and all the reproach of falsehood.” His biographer James Boswell adds: “Sometimes it may proceed from a man’s strong consciousness of his faults being observed. He knows that others would throw him down, and therefore he had better lye down softly of his own accord.” My experience is that when indulged in too frequently, self-criticism is a sign of pride and insincerity. Such behavior costs no effort compared to the hard work of avoiding the admitted faults in the first place (like those people who always talk about dieting). Along these lines, Johnson offers the following advice:
A man cannot with propriety speak of himself, except he relates simple facts; as, “I was at Richmond:” or what depends on mensuration; as, “I am six feet high.” He is sure he has been at Richmond; he is sure he is six feet high: but he cannot be sure he is wise, or that he has any other excellence.
Johnson did not always follow his own rule, but it’s still a good standard worth aiming at.