Valuation is never a simple snapshot of a few key metrics. Rather, it is a much more dynamic and complex question involving vectors that are constantly subject to change. … Merely looking at the price-to-earnings ratio alone for equities (is) grossly oversimplified.
To determine which asset class is “flashing a warning signal” — which is pricier — requires us to ask questions about what will happen in the future. These are events that we do not and cannot know.”
Barry Ritholtz, “Don’t Let A Bad Process Derail Your Investments,” Financial Advisor, February 28, 2017