Mark Twain (2017). “The Complete Works of Mark Twain (Illustrated Edition): Novels, Short Stories, Memoir, Travel Books, Letters, Biography, Articles & Speeches: The Adventures of Tom Sawyer & Huckleberry Finn, Life on the Mississippi, Yankee in King Arthur's Court…”, p.8291, e-artnow
Attributed to Aristotle in Diogenes Laertius "The Lives and Opinions of Eminent Philosophers" translated by C. D. Yonge and Henry G. Bohn (p. 188), 1853.
George MacDonald (2015). “The Complete Novels of George Macdonald (Illustrated): The Princess and the Goblin, The Princess and Curdie, Phantastes, At the Back of the North Wind, Lilith, David Elginbrod, Malcolm, Ranald Bannerman's Boyhood, Wilfrid Cumbermede and many more”, p.8795, e-artnow