Everyone knows entrepreneurs are a little crazy, and a new book claims it's both genetic and very American. In The Hypomanic Edge: The Link Between (a Little) Craziness and (a Lot of) Success in America, author John D. Gartner (left) claims that the personality traits that define entrepreneurial overachievers, like exceptional energy reserves, gut-instinct decision making, and an affinity for taking risks, are symptoms of hypomania, a psychiatric cousin of bipolar disorder. Gartner suggests the U.S. leads in churning out entrepreneurs because this is a nation of immigrants, another group high in hypomanic risk-takers. He uses case studies of historic visionaries like Alexander Hamilton and Andrew Carnegie to support his contention that hypomanics have long been threatening to change the world.