Two economists are sitting on a park bench.
“I’ll pay you $100 if you eat that dog shit” says one
The other economist, being a rational actor, naturally eats the dog shit. He is given the $100.
But then he sees another dog shit. “Well, I’ll pay you $100 to eat that one!”
A second shit is consumed, producing $200 of GDP. The economists are overjoyed at their productivity and earnings.