Warren Buffett makes mistakes too. The 90-year-old billionaire on Saturday admitted he “paid too much” when his Berkshire Hathaway Inc. spent $32.1 billion in 2016 to buy aircraft and industrial parts maker Precision Castparts Corp., its largest acquisition. Berkshire wrote off $9.8 billion of Precision’s value last August, as the coronavirus pandemic sapped demand for air travel and the Portland, Oregon-based unit’s products. In his annual letter to investors, Buffett said he bought “a fine company—the best in its business,” and Berkshire was “lucky” to have Precision Chief Executive Mark Donegan still in charge. But Buffett said he was “simply too optimistic about PCC’s normalized profit potential.” Precision shed more than 13,400 jobs, or 40 percent of its workforce, in 2020, and only recently has begun to improve margins, Berkshire said. “I was wrong … in judging the average amount of future earnings and, consequently, wrong in my calculation of …