This is pretty much it. Thinking rationally, we can see pretty obviously that this is a case of using the past to predict the future. It's never guaranteed to

This is pretty much it. Thinking rationally, we can see pretty obviously that this is a case of using the past to predict the future. It's never guaranteed to work, but since it tends to be the common sentiment shared among so many investors, it does become somewhat self-perpetuating. At the end of the day, the market does move based on sentiments, after all. However, it probably is a good idea to try to shield yourself from potential downsides when this sentiments changes in the future (and it certainly can).