Is The Market Efficient?

I have asked this question a time or two before. But I have thought about it in a different way and have decided for today that the market is not efficient. At least not efficient in the sense that it adheres to some average valuation level.

The problem is the market is overvalued and undervalued for long periods of time. It is hard for an investor to know when it will revert to the mean, and in all likelihood overshoot on the other side.

Overshoot and undershoot are a structural aesthetic of the market. The duration and magnitude of overshoot or undershoot is not well understood.

I would say the market is virtually never efficient. At least not from a valuation perspective.

It seems to me that there are times when the market is overvalued. The implication is market participants are expecting better things in the future. And there are times when the market is undervalued. The implication being market participants are expecting worse things in the future. But throughout, regime changes and overshoot are a function of changing expectations, money flows, fear/greed levels, and liquidity. 

Over and undervaluation point to correlated mistakes.  Paul Samuelson said something to the effect, markets are macro inefficient but micro efficient. That is probably right although it doesn't make much sense.

Just as correlations and assumptions of normal distributions are non-stationary and change over time, so to does the market average valuation line. With that being the case, one would presume that more recent data (valuation levels) would be more relevant for ascertaining the "modern" average valuation level as compared to a longer term mean. This may or may not be a good assumption to make. Only time will tell ('tis the answer to everything).