Suppose you are on a desert island and possess exactly 20 coconuts your neighbor Friday is a fisherman and he is willing to trade to fish for every one coconut that you are willing to give him another neighbor Cowan is also a fisherman and is willing to trade three fish for every one coconut

It seems a good deal, this it could be like old-time, when there is no coin, people traded goods and service for other goods and service, this was the economic, in this particular example it could be something similar, but is the fish is bigger could be traded by two coconuts, in addition, the job of the fisherman is harder and the coconuts are for season.