“I reproach myself for a gross error. But I would reproach myself more if I had persisted in an error after observations revealed it clearly to be that. I made a deal of money in the late 1940s on the bull side, ignoring Satchel Paige’s advice to Lot’s wife, “Never look back.” Rather I would advocate Samuelson’s Law: “Always look back. You may learn something from your residuals. Usually one’s forecasts are not so good as one remembers them; the difference may be instructive.” The dictum “If you must forecast, forecast often,” is neither a joke nor a confession of impotence. It is a recognition of the primacy of brute fact over pretty theory. That part of the future that cannot be related to the present’s past is precisely what science cannot hope to capture. Fortunately, there is plenty of work for science to do, plenty of scientific tasks not yet done.”

February 1985, in William Breit and Roger W. Spencer (ed.) Lives of the laureates
1980s–1990s