When I was a boy of 14, my father was so ignorant I could hardly stand to have the old man around. But when I got to be 21, I was astonished at how much the old man had learned in seven years.

in The Reader's Digest (September 1939), p. 22. Reported as unverified in Respectfully Quoted: A Dictionary of Quotations (1989). This has been widely reprinted and attributed to Twain, but has never been found in his works, though various Twain groups and the Twain Papers staff have searched for it.