The Bodhisatta was once a wealthy merchant. A merchant from the border region, who the Bodhisatta knew only through correspondence, sent a large caravan to trade merchandise with him. While they were in his city, the Bodhisatta lodged these men and gave them spending money. Soon after, the Bodhisatta sent his own caravan to trade with the border merchant, but he did not provide food, lodging, or even simple courtesy to the Bodhisatta’s men.
The next time the border merchant sent a caravan to trade with the Bodhisatta, his men told the travelers to set up camp outside the city and said provisions would be sent later. But instead, the men came late at night and looted the caravan, taking everything of value, including their wagon wheels. Later, when the Bodhisatta heard what his men had done, he told the crowd around him that ungrateful people get what they deserve.
In the Lifetime of the Buddha
Anathapindika, a wealthy supporter of the Buddha known for his extreme generosity, told the Buddha that recently he had treated some workers of a merchant from the border region very generously, but his men had not received the same courtesy in return, so when the merchant sent a second caravan, his men stole everything from it.
The Buddha told Anathapindika this story so he knew that he himself once had the exact same interactions with an earlier birth of the border merchant.