On a warm September night in 2002, former acquaintances Alexis Maybank and Alexandra Wilkis reconnected at a mixer for new students at Harvard Business School. Alexis had just ended a four-year run at eBay during the dotcom boom and bust. Alexandra had just spent three years as an investment banker at Merrill Lynch. Now they were entering the country’s top training ground for future titans of Wall Street and the Fortune 500. Little did either suspect that five years later, they’d become famous not in finance or consulting or corporate management, but at the bleeding-edge intersection of fashion and technology. Gilt Groupe – launched by Alexis, Alexandra, and three colleagues in 2007 – is one of the most fascinating startups of recent years, with a valuation of more than $1 billion. And it all began with one bold idea: to bring sample sales online and change the way millions shop. As Alexis and Alexandra write about the day Gilt.com went live: “We had...