I believe that over reliance on historical patterns and market moves is bunk and should not be considered an important indicator of future trends. Market commentary and analysis, esp. in the financial press and TV, unfortunately gravitates to this thinking because they need some reference to anchor their opinions and using historical markers makes you seem like a serious person whereas those who say "I don't know what the future will behold" are dismissed or marginalized. Many bulls point to the early 1980s or the 1990s and therefore believe the market has further upside. Conversely, many bears point to 1930 or post-bubble Japan as indicators of the trouble we will face and therefore you should either stay on the sidelines or short an already frothy market. However, both sides are wrong. History doesn't repeat itself and therefore it cannot be used as guide to what may happen in the future. Although you might think that some can predict the future and know what will happen, this is merely an artifact of survivorship bias. The ones who got it "right" are the ones you remember and the ones who got it wrong fad away. These supposed seers attract a lot of press and attention until their predictions turn out wrong. Then we move onto a new set of "experts". Rinse and repeat. Moreover, the markets have changed considerably from past reference points. Trading is driven by technology and the number of participants is only increasing, reducing any edge traders once had. Concepts like mean reversion and other arbitrage strategies like pairs trading are nice in theory and as academic papers, but are flawed as actionable investments. What once might have worked using backtesting doesn't mean it will perform as expected in real time.