The more enthusiastic investors become about the stock market in the long run,....

Even though investors all know they're supposed to buy low and sell
high, in practice they often end up getting it backwards. Graham's
warning in this chapter is simple: "By the rule of opposites," the more
enthusiastic investors become about the stock market in the long run,
the more certain they are to be proved wrong in the short run.

The more enthusiastic investors become about the stock market in the long run,....