How to avoid becoming a bag holder
The first step is to control your own biases. That doesn't mean you study what all the behavioral biases are and try to identify when they're affecting you. You have to create an objective framework through which you evaluate your investments.
Use a checklist when initially evaluating the investment. Track what management says on conference calls and compare it to actual results. Reevaluate everything at least annually. If sales and returns are falling, debt is rising, and insiders are unloading their shares, there's probably something wrong. Learn when to sell stocks and stick to it.
Of course, the best way to avoid becoming a bag holder is to skip the value traps in the first place. Stocks with loads of debt, no growth, and bad management can look like great values, but, usually, they aren't. Additionally, think long and hard about investing in a dead industry. For every Best Buy (BBY -1.68%), there are 10 Circuit Cities.