When Brian Chesky was pitching venture capitalists to invest in Airbnb, one of the people he consulted was the entrepreneur and investor Sam Altman, who later became the president of the Y Combinator start-up accelerator. Altman saw Chesky’s pitch deck and told him it was perfect, except that he needed to change the market-size slide from a modest $30 million to $30 billion. “Investors want B’s, baby,” Altman told Chesky. Of course, Altman wasn’t telling Chesky to lie; rather, he argued that if the Airbnb team truly believed in their own assumptions, $30 million was a gross underestimate, and they should use a number that was true to their convictions. As it turns out, Airbnb’s market was indeed closer to $30 billion.