What's the hardest part of building a hot startup? In Part II of his Founder Stories interview, Foursquare CEO Dennis Crowley tells Chris Dixon it's not building the product, it's building the company that builds the product. The product is easy. Crowley and his team have been thinking about the product for years. "The hard part is building the machine that builds the product," he says. Foursquare has grown from 2 to 50 people, moved into bigger offices, and had to build a backend system that can support millions of users. But all of that was behind the scenes. "This is our year to build all the stuff we have been thinking about," he declares.