"[von Neumann] spent the last year of his life in Walter Reed Hospital in Washington, D.C., where he surprised and dismayed friends and family by seeking out a priest for counsel. His brother explains this away as merely an effort to find intellectual companionship; his daughter Marina affirms, to the contrary, that von Neumann was taking up Pascal's Wager—betting on the existence of God, since he couldn't lose by being wrong: 'My father told me, in so many words, once, that Catholicism was a very tough religion to live in but it was the only one to die in.'
"Whatever his spiritual state may have been, we know that he was distressed by the disease's effect on his mind. An old joke among mathematicians says, 'Other mathematicians prove what they can; von Neumann proves what he wants,' but in the last weeks of his life he felt his mind rapidly deteriorating. What had always come so easily to him—almost supernaturally easy—became difficult and then impossible. Marina von Neumann told George Dyson that near the end her father asked her 'to test him on really simple arithmetic problems, like seven plus four, and I did this for a few minutes, and then I couldn't take it anymore.' Even as von Neumann stumbled over the most elementary sums, he never lost his awareness that mathematics was important and that he had been marked from childhood by the astonishing fluency with which he could do it. Marina von Neumann fled the hospital room: in George Dyson's words, she could not bear to watch her father, one of the greatest minds of the 20th or any other century, 'recognizing that that by which he defined himself had slipped away.'"
Alan Jacobs, "The man who delivered the computer," Books and culture (September/October 2012): 38.