Noted: If you are thinking, “Wait, that’s just nuts,” think again about the nature of risk. We have learned to protect and restore rivers in our cities, says Adrian Treves at the University of Wisconsin, even though floods sometimes destroy homes and drown people. We cherish trees on urban streets and in parks even though branches sometimes fall on our heads. For that matter, we let cars dominate city streets, though they kill more than 4,700 pedestrians in the United States every year (and many times more in India).