Translation: Economist 1 needed the pile of shit to be eaten but at that time was unwilling to do it for $100, Economist 2 is willing and is willing to take Economist 1's good faith agreement to return a $100 favor later on. Probably eating the pile of shit is not as expensive to Economist 2 as $100 at that time. Later Economist 2 discovers a pile of shit that he is unwilling to eat for $100, it's a more expensive exercise, perhaps to Economist 2 this pile of shit is worse, or he's not in the right state to do it. Economist 1 now considers this exercise worth doing for $100 and does so. They are both left in a state where they each had a pile of shit eaten on their behalf and they are otherwise net 0 in costs. Instead of $100 they could possibly have agreed between them their own currency of made up IOUs. They did indeed end up producing $200 of equivalent work. Without an ability to create a credible debt contract between them, the piles of shit would not have been eaten, and presumably they would both have been worse off. Unless as the joke implies they are complete idiots who ask people to do worthless tasks. In which case, ha ha, I get it.