Benjamin Graham (teacher of Warren Buffet / Prof. at Columbia University)
„The explanation cannot be found in any mathematics but it has to be found in investor psychology” (B. Graham)
Furtheron he goes "You can have an extraordinary difference in the price level mereley because not only speculators but investors themselves are looking at the situation through rose-colored glasses rather than dark-blue glasses. It may well be true that the underlying psychology of the American people has not changed so much and what the American people been waiting for many years has been an excuse for going back to the speculative attitude which used to characterize them from time to time. IF HISTORY counts for anything than the stock market is much more likely than not at a point where REAL DANGER […]” This quote from Benjam Graham stems FROM A TIME BEFORE the .com-bubble, the chinese Stock-market bubble in 2007 and 2015, etc.
Another quote from one of his assistants, Irving Kahn (read more here / http://basehitinvesting.com):
Irving Kahn was a disciple of Ben Graham (he was an employee at Graham’s firm), so it can be useful to listen to his ideas. Kahn began in the investment field in 1928 (imagine being able to talk with someone who was 25 years old at the beginning of the Great Depression!). Kahn has built a remarkable investment career by following the teachings and principles of Graham.
Investing is an art, not a science / “All the kids that believe in equations and rules, will learn more as they get older.”