M. Scott Peck (2002). “The Road Less Traveled, 25th Anniversary Edition: A New Psychology of Love, Traditional Values, and Spiritual Growth”, p.15, Simon and Schuster
Richard P. Feynman's letter to Koichi Mano (February 3, 1966), as quoted in "Perfectly Reasonable Deviations from the Beaten Track: The Letters of Richard P. Feynman" edited by Michelle Feynman and Timothy Ferris (pp. 198, 201), April 5, 2005; also quoted in "Wise Man" by Freeman Dyson, www.nybooks.com. October 20, 2005.