To wit:

"There is also just the simple issue that markets are very extended above their long-term trends, as shown in the chart below. A geopolitical event, a shift in expectations, or an acceleration in economic weakness in the U.S. could spark a mean-reverting event which would be quite the norm of what we have seen in recent years."

This analysis is what led us to take action for our RIAPRO subscribers last week (30-Day Free Trial), as we added a 2x-short S&P 500 index fund to Equity Long-Short Account to hedge our longs (GOOG, CRM, NVDA, EMN, IVV, RSP) against a potential mean reversion.