Understanding Ricardo

There is a theory in economics which shows that it can be beneficial for two parties to trade in a goods or services, even if one of the parties has a lower relative cost of producing all goods and services. In other words if India can produce both rice and oil at a lower cost than Bangladesh, it still makes sense for India to buy rice from Bangladesh and sell oil to Bangladesh.
Apparently what matters is not the absolute cost of production but the opportunity cost, which measures how much production of one good is reduced to produce one more unit of the other good.
Counterintuitive. But it is one of the cornerstones of international trade theory.