Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.15, St. Martin's Press
Ralph Waldo Emerson, Robert Ernest Spiller, Alfred Riggs Ferguson, Joseph Slater, Jean Ferguson Carr (1971). “The Collected Works of Ralph Waldo Emerson: Nature, addresses, and lectures”, p.68, Harvard University Press
Adele Faber, Elaine Mazlish (2012). “Siblings Without Rivalry: How to Help Your Children Live Together So You Can Live Too”, p.228, W. W. Norton & Company