Address at the Sorbonne, Paris, 23 Apr. 1910. Richard M. Nixon quoted this passage in his address to the nation announcing his decision to resign the presidency, 8 Aug. 1974. See Theodore Roosevelt 1; Theodore Roosevelt 2; Theodore Roosevelt 5
"Built to Learn: The inside story of how Rockwell Collins became a true learning organization". Book by Cliff Purington, Chris Butler, and Sarah Fister Gale, p. 171, 2003.
H. Jackson Brown Jr. (2007). “Complete Life's Little Instruction Book: 1,560 Suggestions, Observations, and Reminders on How to Live a Happy and Rewarding Life”, p.286, Thomas Nelson Inc