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
Elbert Hubbard (2009). “Love, Life & Work: Being a Book of Opinions Reasonably Good-Natured Concerning How to Attain the Highest Happiness for One's Self with the Least Possible Harm to Others”, p.133, The Floating Press