A recent post from the excellent Mathematical Investor blog questions whether the use of chart patterns and technical analysis truly offers value in financial markets. The authors point out how easy it is to manipulate information to look significant (commonly encountered when an "analog" to the current time period is found in a previous historical period). Indeed, it's possible to find historical analogs to any market behavior simply because the search space over the course of financial history is so large. This is classic overfitting: the similarities of today and the past are likely to be chance artifacts.