Warren Buffett is not a fan of portfolio diversification. He once indicated it meant that someone didn’t know what they were doing. “Diversification is a protection against ignorance,” he wrote to shareholders.Of course, Buffett’s Berkshire Hathaway (NYSE:BRK-A, BRK-B) owns dozens of companies, though that’s more a result of its size than breaking Buffett’s rule. He would like to own fewer companies but deploying hundreds of billions of dollars requires buying more stocks.Still, for the average investor loo ...