We can see from the many “bubbles” that have occurred in the stock market (or in the prices of specific stocks) that investors do not always value stocks rationally (we have seen this, for example, in the late 1920s and in the tech stock bubble of the early 2000s). The most common non-rational factor is the fear of losing out while others get rich. People see that the stock market in general (or a particular stock) is going up in price. They know that others are making money and they fear that they will be left behind. When they buy stocks, they are assuming that the prices will continue to rise simply because they have been rising up to this point. They are also acting based on the fear that they will be the only ones who did not make money during a boom. In both cases, they are acting not on rational factors connected to the fundamentals of specific companies. Instead, they are valuing the stocks based solely on hope and/or fear.