Whether you buy direct stocks, or you invest in a mutual fund / ETF, you are usually buying a share of a revenue generating business. The price of a stock is much more volatile than the fundamentals of that business. This provides opportunity and risk for investors. During crashes, stock prices will often fall further than current and future earnings, which creates value and a buying opportunity. Conversely, an increase in stock price doesn’t always mean its revenue is going to grow at the same rate, this can lead to stocks being overvalued. As an investor you need to learn the difference between price and value.