Uber just became one of the most valuable tech startups in history. Co-founder and CEO Travis Kalanick announced that investors are pouring another $1.2 billion into Uber in a funding round that values the five-year-old company at $17 billion. Though nine and 10-figure deals have become common enough in Silicon Valley to seem almost normal, the news may leave many people out in the real world scratching their heads. Does Uber–an app-ified version of the cab business–really need that much money? Given the scope of Uber’s ambition, it just might.