A man stood on the bridge of a great ocean liner as it cut the Atlantic at twenty-five knots. A signal sounded. All through the ship, at the turn of a lever, the watertight compartments swung shut, sealing the hull into separate cells. The captain beside him called it the chief factor of safety, the thing that let the vessel take a blow to one part and stay afloat.

He carried that picture to Yale. In the spring of 1913, a year after the Titanic went down, the man, William Osler, stood before the students and told them each of them was a finer vessel than any liner, bound on a longer voyage. Learn to run on the same principle, he said. Seal off the dead yesterday. Seal off the unborn tomorrow. Live in day-tight compartments, and do the work of the day in front of you.