Shortly before the opening of Nasdaq trading on Friday, Elon Musk stepped in front of a cheerful crowd at SpaceX's company town in Texas. His rocket maker was about to hit the public market at a valuation of around $2 trillion, instantly becoming the sixth most-valuable U.S. company. Musk, weeks shy of his 55th birthday, told staffers that, in the early days of the company, he gave it "less than 10% chance of succeeding." "If people had told me this was going to happen, I was like, man, you