Value investors don’t believe in the efficient-market hypothesis, which says that stock prices already take all information about a company into account, so their price always reflects their value. Instead, value investors believe that stocks may be over- or underpriced for a variety of reasons.
For example, a stock might be underpriced because the economy is performing poorly and investors are panicking and selling (as was the case during the Great Recession). Or a stock might be overpriced because investors have gotten too excited about an unproven new technology (as was the case of the dot-com bubble). Psychological biases can push a stock price up or down based on news, such as disappointing or unexpected earnings announcements, product recalls, or litigation. Stocks may also be undervalued because they trade under the radar, meaning they’re inadequately covered by analysts and the media.