Answer:
the invisible hand
Explanation:
The invisible hand is a concept developed by Adam Smith and it refers to the forces that determine the equilibrium of a market. This concept is based on the idea that both consumers and suppliers will seek their own benefit and self interest when making a transaction, but the invisible hand will help to allocate resources efficiently.
In this case, the invisible hand refers to the unexpected benefits generated by the couple reopening the grocery store. Both the owners and their customers act selfishly, but it is in their best interest that the grocery store keeps working and expanding. The whole town wins in this situation, the new owners of the grocery store make a profit and their customers don't have to travel 20 miles.