Buying stock is trading future money than money today which is a real and meaningful trade.  On the other side, I might want a new car, which means I want money, which means I want to sell stock.<p>Even stock to stock transitions can be meaningful as Bill Gates had a lot of MS stock and wanted a hedge so he sold stock. What he got was probably worth &#x27;less&#x27; the diversification was valuable to him making the transaction a net positive.