In 2007, the founder of Facebook, Mark Zuckerberg, knew that he needed help. His social-network site was growing fast, but, at the age of twenty-three, he felt ill-equipped to run it. That December, he went to a Christmas party at the home of Dan Rosensweig, a Silicon Valley executive, and as he approached the house he saw someone who had been mentioned as a possible partner, Sheryl Sandberg, Google’s thirty-eight-year-old vice-president for global online sales and operations.
