John W. Campbell, in a letter to L. Ron Hubbard, January 23, 1939:
All human beings like wishes to come true. In fairy stories and fantasy, wishes do come true. Adults with childish minds (average “adult” has the mind of a 14 year-old) don’t dare read “fairy stories”, because their minds are afraid to acknowledge their interest in anything childish — they subconsciously realize their mental immaturity, and, as a defense mechanism, avoid childish things.
Your true adult, with fully developed mind, can enjoy fantasy whole-heartedly if it’s written in adult words and thought-forms, because, being absolutely confident of his own mental capacity, he doesn’t have any sense of embarrassment if caught reading “childish stuff”.
Found in The John W. Campbell Letters, Volume 1