He also admitted mistakes of his own, saying he had closed a troubled credit card business, which had been his idea, and had given too much time to turn around the NetJets business, long a burden.

Closing the letter, Mr. Buffett, ever the cheeky salesman, invited shareholders to his company’s annual meeting on May 1 in Omaha — promising to play table tennis for spectators and urging them to buy goods and services from his companies, and ending, "P.S. Come by rail."