Since making a new all-time high on March 27, the S& 500 has risen 7%. That may make some investors and pundits nervous, but there is little to fear with regard to new highs per se: Stock prices do not mean-revert -- i.e., rather than fluctuating around an average, stock prices tend to drift upwards over time.
Stock valuations, on the other hand, are an entirely different matter. Price-to-earnings ratios, including the cyclically adjusted price-to-earnings ratio, or CAPE, certainly do revert to the mean. How is the market doing on that front?