Some experience of popular lecturing had convinced me that the necessity of making things plain to uninstructed people, was one of the very best means of clearing up the obscure corners in one’s own mind.
‘Preface’. In Man’s Place in Nature and Other Anthropological Essays. Collected Essays (1894), Vol. 7, Preface, ix.
I find that the only time I really learn anything is when I have to teach it to someone.