Last weekend, in Omaha, Nebraska, at the annual meeting of Warren Buffett’s holding company, Berkshire Hathaway, Buffett announced that at the end of this year he will give up his post as C.E.O. According to reports, some people in the crowd cried at the news. Given that the attendees were nearly all Berkshire Hathaway shareholders, this reaction was perhaps unsurprising: if you bought a hundred dollars of Berkshire stock in 1964, just before Buffett took over the company, by the end of last yea...