… is from page 93 of Milton Friedman’s 1985 lecture “My Evolution as an Economist,” in Lives of the Laureates , William Breit & Roger W. Spencer, eds. (3rd ed., 1995):
[M]y life as an economist has been the source of much pleasure and satisfaction. It’s a fascinating discipline. What makes it most fascinating is that its fundamental principles are so simple that they can be written on one page, that anybody can understand them, and yet that very few do.