What is comparative advantage?

Comparative advantage is the ability of any given individual or group to produce goods or services at a lower opportunity cost than others. If you are equally good at sewing that pays $15 an hour and medicine that pays $40 an hour, and have a friend who will do sewing for $20 an hour and cannot do medicine for her or himself, comparative advantage means that focusing on doing medicine will yield you $20 more an hour if you hire your friend to do sewing while you practice medicine than if you decided to do both sewing and medicine. The law of comparative advantage is the reason that economic actors engage in willing trade as each seeks to maximize their potential.