Two economists are walking down the sidewalk. One looks down and sees a 100 dollar bill on the ground in front of them. "Look," he exclaims to his friend, "a $

Two economists are walking down the sidewalk. One looks down and sees a 100 dollar bill on the ground in front of them. "Look," he exclaims to his friend, "a $100 bill!" "Nonsense," remarks the other, "if there was a $100 on the sidewalk, someone would have already seen it and picked it up."