Diversification ranks among the most important components of many investment strategies. However, one of the world's greatest investors isn't gung ho about the idea. Warren Buffett once said, "Diversification is protection against ignorance.

Warren Buffett is rightfully considered one of the greatest investors of our time. Over 60 years of running Berkshire Hathaway (NYSE:BRK-A)(NYSE:BRK-B) has produced returns twice those of the S&P 500.

Warren Buffett paid tribute to the late Charlie Munger, gifted more than $6 billion to good causes, and sold $133 billion of stocks in nine months.

Another recent buy for Berkshire was an addition to its Sirius XM Holdings ( SIRI 1.18%) stake. Berkshire has been invested in Sirius' Liberty Media tracking stock since 2016, but increased its stake in Sirius after its simplification merger with the tracking stock this past September.

The Berkshire Hathaway chief sticks to a winning investing formula, but he does not sit still.

Warren Buffett's recent moves raise questions about Berkshire Hathaway's strategy as it amasses a record cash pile amid market highs.

Coca-Cola has a proven track record of global brand power and a reliable dividend. Domino's is operating smoothly and growing despite global economic volatility. Both of these stocks trade at the same P/E ratio,

Arguably the world's greatest stock picker isn't picking many stocks these days. Warren Buffett has been a net seller of stocks for eight consecutive quarters. There's a reason Buffett isn't buying many stocks -- and it's the same reason he ranks among the greatest investors of all time.