Why should exchange be so universal among mankind? Fundamentally, because of the great variety in nature: the variety in man, and the diversity of location of natural resources. Every man has a different set of skills and aptitudes, and every plot of ground has its own unique features, its own distinctive resources. From this external natural fact of variety come exchanges; wheat in Kansas for iron in Minnesota; one man’s medical services for another’s playing of the violin. Specialization permits each man to develop his best skill, and allows each region to develop its own particular resources. If no one could exchange, if every man were forced to be completely self-sufficient, it is obvious that most of us would starve to death, and the rest would barely remain alive. Exchange is the lifeblood, not only of our economy, but of civilization itself.

- Murray Rothbard