Paul Samuelson on comparative advantage

Nobel laureate Paul Samuelson (1969) was once challenged by the mathematician Stanislaw Ulam: "Name me one proposition in all of the social sciences which is both true and non-trivial."  

It was several years later than he thought of the correct response: comparative advantage.  "That it is logically true need not be argued before a mathematician; that is not trivial is attested by the thousands of important and intelligent men who have never been able to grasp the doctrine for themselves or to believe it after it was explained to them."

~ Paul Samuelson