Don't think about this one too hard - especially if you work in an office - or you'll probably end up crying.
Two economists are walking in the countryside when they come upon a humongous cow pat. The first, feeling mean for a moment, says "Hey, I dare you to eat that pile of shit for £100."
The second economist recalls that he chose to go into academia and could use every spare pound he can get his hands on, so he agrees to the dare, gets down on his knees, and chows down.
They continue their hike when they happen upon another cow pat. The second economist decides to get his own back. "Hey, I dare you to eat that pile of shit for £100."
The first economist considers that the sight of watching the second eat the first pile of shit wasn't as rewarding as he had expected, and he is feeling loss aversion for his spent £100. So he agrees, gets down on his knees, and gobbles up the shit.
They continue walking and the first economist says: "Hey, I gave you the £100 that you gave straight back to me, but we both ate shit. I feel like we achieved less than nothing."
"Don't you remember your training?" replies the second. "Between us, we increased GDP in the service sector by a whole £200!"