An economist and his friend were walking down the street, when they spied a 100$ bill lying on the pavement. The economist strode past without a second look. Hi

An economist and his friend were walking down the street, when they spied a 100$ bill lying on the pavement. The economist strode past without a second look. His friend tugged on his sleeve, "Why didn't you pick it up! That was 100$ !" The economist snorts, and says, "If that was a real 100$ bill, someone else would have picked it up already."