An economist and a stock trader are talking a random walk down Wall Street

The trader spots a fresh $100 bill, "Oh look! A $100!" he exclaims as a reaches down to pick it up. But the economist stops him, "No wait, that's a fake $100." "But how do you know?" the trader replies. The economist replies haughtily, "Because if that were a real $100, someone would have already picked it up"

Then the trader said "I'll bet you a billion dollars it's real, and give you 10 thousand to one odds."

The economist calculated the EV and accepted the bet.

The trader picked up the bill, but when he turned it over, the face on the bill was of the wrong man. That man was Albert Einstein.

At that moment, a black swan descended from the sky and landed on the economist's shoulder and shed a single tear.

Fortunately, Barack Obama appeared with a bag of $10 Trillion in taxpayer money to bail out the trader and everyone laughed and cheered and high-fived each other.