Kate Losse was a grad school refugee when she joined Facebook as employee #51 in 2005. Hired to answer user questions such as "What is a poke?" and "Why can't I access my ex-girlfriend's profile?" her early days at the company were characterized by a sense of camaraderie, promise, and ambition: Here was a group of scrappy young upstarts on a mission to rock Silicon Valley and change the world. Over time, this sense of mission became so intense that...