The origin of the expression is as follows. It was said that a group of fishermen caught a large number of turtles. After cooking them, they found out at the communal meal that these sea animals were much less edible that they thought: not many members of the group were willing to eat them. But Mercury happened to be passing by –Mercury was the most multitasking, sort of put-together god, as he was the boss of commerce, abundance, messengers, the underworld, as well as the patron of thieves and brigands and, not surprisingly, luck. The group invited him to join them and offered him the turtles to eat. Detecting that he was only invited to relieve them of the unwanted food, he forced them all to eat the turtles, thus establishing the principle that you need to eat what you feed others.
via https://medium.com/incerto/why-each-one-should-eat-his-own-turtles-equality-in-uncertainty-e2b2ee3bcddf