"When I was a student at the University of Chicago, where I was a direct student of in the classroom, and an indirect student of Frank Knight, I could not learn why price should equal marginal cost. Even when I got to Harvard in 1935, I went around asking everybody: “What is the proof that this is so?” Of course, I did not know the 1892–1893 work of Vilfredo Pareto in which he essentially shows that a perfectly competitive equation system gives you the necessary and sufficient condition, not for ethical optimality—he was always a little slippery on that problem—but for what came to be called Pareto optimality so that there is no avoidable deadweight loss. I think I had most to learn from Abba Lerner, although I, of course, worked it out for myself."