As Dow tanks, here is Warren Buffett on the biggest puzzle for investors

When Warren Buffett recently bought back nearly $1 billion in Berkshire Hathaway stock, he based the buyback on a share price that was trading below "intrinsic value." With public company values elevated after 10 years of a bull market, valuation analysis like this is important. But intrinsic value is not an easy concept to explain or master, and Buffett has played his cards to his vest when discussing the idea.