As arguably the greatest investor of all time, Warren Buffett has made relatively few mistakes in his decades of investing. But Kraft Heinz (KHC 0.41%) was one of them. According to Buffett, Heinz overpaid for Kraft in 2015, which was a deal that Buffett's Berkshire Hathaway (BRK.A 0.95%) (BRK.B 1.11%) was involved with and mistakenly promoted.Kraft Heinz stock has lost two-thirds of its value over the last decade and now sits at five-year lows. However, Berkshire Hathaway continues to own about 27% of the ...