His uncertainty forces the enthusiast to puff up his truths, of which he feels none too sure, and to win proselytes to his side in order that his followers may prove to himself the value and trustworthiness of his own convictions. … Only when convincing someone else does he feel safe from gnawing doubts.

Carl Jung (1875-1961) Swiss psychologist

“The Relations between the Ego and the Unconscious” (1.2) (1928) [tr. Hull (1953)]