One of Warren Buffett's best tips for investing amid volatility is to "be fearful when others are greedy, and be greedy when others are fearful." He offered this advice in a 2008 opinion piece for The New York Times, when investors were discouraged and pessimistic during the Great Recession.

This single position generates over $800 million in annual income for Berkshire Hathaway. Demand for this company remains resilient in difficult economic conditions, something investors might appreciate today.

Specific regulatory filings, along with the Oracle of Omaha's investing habits, help narrow down which secret stock Buffett may be purchasing.