The real tragedy of Oppenheimer’s life was not the loss of his security clearance but his failure to be a great scientist. For forty years he put his heart and soul into thinking about deep scientific problems. With the single exception of the collapse of massive stars at the end of their lives, he did not solve any of these problems. Why did he not succeed in scientific research as brilliantly as he succeeded in soldiering and administration? I believe the main reason why he failed was a lack of Sitzfleisch. Sitzfleisch is a German word with no equivalent in English. The literal translation is “Sitflesh.” It means the ability to sit still and work quietly. He could never sit still long enough to do a difficult calculation. His calculations were always done hastily and often full of mistakes. In a letter to my parents quoted by Monk, I described Oppenheimer as I saw him in seminars:
He is moving around nervously all the time, never stops smoking, and I believe that his impatience is largely beyond his control.