National Treasure A psychologist explains how entrepreneurs started it all.

It's no secret that the U.S. is a nation of entrepreneurs bold enough to risk it all, go after an idea and find success on the other end. But maybe we need to start giving credit where credit's due. In his book, The Hypomanic Edge: The Link Between (a Little) Craziness and (a Lot of) Success in America, clinical psychologist John D. Gartner introduces a revolutionary theory that links hypomania--a medical condition resulting in elevated mood and increased activity--with our immigrant ancestors and the entrepreneurial accomplishments of today.

Entrepreneur: Can you explain your theory?

John D. Gartner: America is rich in hypomanics--that's our greatest natural resource. It's the temperament we find in entrepreneurs that helps them make discoveries, win support for new ideas and drive progress. Why are we so rich in hypomanics? We're a nation primarily populated by immigrants. They have a certain amount of energy, optimism and tolerance [for risk]. Immigration was a risk very much like starting a new business.