Krugman and Keynes, are walking in a forest when they come across a pile of shit. Krugman says to Keynes, "I'll pay you $100 to eat that pile of shit." Keynes takes the $100 and eats the pile of shit. They continue walking until they come across a second pile of shit. Keynes turns to Krugman and says, "I'll pay you $100 to eat that pile of shit." Krugman takes the $100 and eats a pile of shit. Walking a little more, Krugman looks at Keynes and says, "You know, I gave you $100 to eat shit, then you gave me back the same $100 to eat shit. I can't help but feel like we both just ate shit for nothing." "That's not true," responded Keynes. "We increased the GDP by $200!"