Warren Buffett is the CEO of the Berkshire Hathaway (NYSE: BRK.A)(NYSE: BRK.B) holding company, where he helps manage a $287 billion portfolio of stocks, in addition to numerous privately held subsidiaries.

Such a precipitous increase in the value of U.S. equities has stirred up the usual cacophony of equity-bears screaming “bubble!” “Bubble” is a popular term, but, as it turns out, is rather ill-defined and fuzzy.

One thing for certain is that financial markets face more uncertainty than usual right now. So it’s tougher to forecast economic and political trends, and to model investment and business risk based on those expectations, at a time that seems more of a major upheaval than a momentary shift.