Most financial principles and theories have a degree of good sense to them. It may be a large degree, but it never comes close to being absolute. None of them ever has the comforting reliability of Euclid’s comment about the length of the hypotenuse of a right-angled triangle. Consider the observable occurrence and reoccurrence of what economists traditionally call the business cycle. It exists, certainly enough. Stocks never go so high that they don’t fall down, and never sink so low that they don’t eventually go back up again. But the duration of this cycle is figured by some at the mystic and Biblical figure of seven years, and sometimes at six. However, there have been periods when it worked out to other numbers of years, such as three, two, or half a year. Or take the period of two and a half years preceding the morning on which these words happen to be written. (Summer, 1949.) While events of world importance have been taking place, the stock market has done nothing but drift listlessly a little lower, from prices which could be considered low to begin with, in view of corporate earnings at that time. Thus the riddle is propounded: can such a pattern be termed predictable?

It is not likely that this riddle will ever be conclusively solved. It is fair to point out, however, that the tendency of the human heart is to plump for the idea that there is a sensible order in the rise and fall of prices, whether the evidence is good or nonexistent. People do not care for the idea that any important activity which affects them is as beyond their control as a pair of dancing dice. — Fred Schwed Jr. (source)

One of the first lessons I heard about pendulums and the swing of investor behavior regarded something I was taught in the early 1970s: the three stages of a bull market. These succinctly capture the essence of investor psychology.

The first stage comes when a few people begin to realize that there will be improvement. The second stage occurs when most people realize that improvement is already taking place. The third stage comes when everyone thinks that things will be getting better forever. Clearly, the first is early; the last is laughably late. One of my favorite adages – perhaps my favorite of all – is that what the wise man does in the beginning, the fool does in the end. So it’s the buyer in the third stage – who buys when optimism is incorporated, under the assumption that things will always get better – who pays the price. — Howard Marks (source)