When I was eleven years old, my friend Billy Rohmann often came over to my house on Saturdays. We usually made a pizza for lunch. I remember very little of who bought the pizza mix or how we made the pizza. But I do remember how we divided it between uso We flipped a coin to determine who would cut the pizza in half. After it was cut, the one who had not done the cutting would pick the half that he wanted. We both had seemingly insatiable appetites for pizza, and each would have been glad to eat the whole thing. Yet we never fought about the shares that we assigned to ourselves in this way.