“In summary, people trade for both cognitive and emotional reasons. They trade because they think they have information when they have nothing but noise (Orient Paper), and they trade because trading can bring the joy of pride. Trading brings pride when decisions turn out well, but it brings regret when decisions do not turn out well. Investors try to avoid the pain of regret by avoiding the realization of losses, employing investment advisors as scapegoats, and avoiding stocks of companies with low reputations."
Meir Statman ("Investor Psychology and Market Inefficiencies," Equity Markets and Valuation Methods, The Institute of Chartered Financial Analysts, 1988)
"Graham's conviction rested on certain assumptions. First, he believed that the market frequently mispriced stocks. This mispricing was most often caused by human emotions of fear (dilution, restatements and auditor issues) and greed. At the height of optimism, greed moved stocks beyond their intrinsic value, creating an overpriced market. At other times, fear moved prices below intrinsic value, creating an undervalued market."
Robert G. Hagstrom, The Warrent Buffet Way
Any time you buy or sell a stock, you should be buying and selling irrational behavior. You should buy shares when they are irrationally cheap and sell them when they are irrationally expensive. Those are subjective concepts but in the end they work. Certainly in hindsight it's obvious when things are absurdly cheap or absurdly expensive.
People typically give too much weight to recent experience and extrapolate recent trends that are at odds with long-run averages and statistical odds. They tend to become more optimistic when the market goes up and more pessimistic when the market goes down.
For quite a period we can say U.S.-Chinese stocks are way undervalued and are traded at bankruptcy prices. Why? Because of in general misplaced fear. Short sellers like fear and will do anything to support it. So prices are slaughtered even more. Look for stocks that are likely to grow more than 20% the coming years, have almost no debt and are investor friendly.
Disclosure: No positions