With Zoom , Fortune magazine extends one of its most successful franchises, 40 Under 40, to bring you original insight on the best-kept secrets of top entrepreneurs, business leaders, and rising tech stars. Discover how Zappos CEO Tony Hsieh built a uniquely attractive corporate culture, how Under Armour founder Kevin Plank took on Nike, and what Marissa Mayer told herself before leaping from a safe post at Google to the high-risk top job at Yahoo...