Albert Einstein (2016). “The Albert Einstein Collection: Essays in Humanism, The Theory of Relativity, and The World As I See It”, p.116, Open Road Media
David Hume (1874). “A Treatise on Human Nature: Being an Attempt to Introduce the Experimental Method of Reasoning Into Moral Subjects; and Dialogues Concerning Natural Religion”, p.534
"Some thoughts on the real world by one who glimpsed it and fled". Bill Watterson's commencement speech at the Kenyon College in Gambier, Ohio, www.graduationwisdom.com. May 20, 1990.