Wayfair was founded with one goal in mind: to get as big as possible. Next stop: $1 billion. Niraj Shah and Steve Conine were at a loss.They felt they had lost their momentum. Four years earlier, the two college friends had sold Spinners, an IT consulting business, for $10 million. But their second venture, Simplify Mobile, which made mobile-phone software for corporate users, never got off the ground. Almost a year's worth of hard work was gone, without much to show for it. So as they considered their next move, Conine and Shah were determined to think big—really big. "We had aspirations," says Shah. It took a while, but soon they felt they had found something really exciting: birdhouses. Or, to be more specific: a website that sold birdhouses. Bear in mind that this was 2002, when public sentiment and the Dow Jones index held that the heyday of e-commerce had come and gone. But that wasn't what Shah and Conine were seeing. The two, for example, were i...