Warren Buffett's investor letter may be his last as Berkshire Hathaway's CEO: "I'm 'going quiet.'" CBS NewsWarren Buffett: ‘I'm going quiet' CNNWarren Buffett will no longer write annual letter, speak at Berkshire Hathaway shareholder meeting Yahoo FinanceWarren Buffett's Berkshire Hathaway Farewell: ‘I'm Going Quiet' The New York Times