<prompt> Human: What is stopping someone with say 50,000 to invest from purchasing a stock that is essentially guaranteed not to drop within that day and then selling it once it increases slightly. For instance, if someone bought 1000 shares of Microsoft at 40 a share what is stopping them from waiting until it goes up to just 40.50 a share or 41 a share and then selling making 1000-500 instantly? There is a trading fee, but from what can be seen the trading fee would not be of substance when trading this many stocks. Also if there is nothing stopping them why wouldnt everyone do this? There is some risk if the stock drops, but what is being reffered to is about stocks like Microsoft, Apple or something of that nature that one can be fairly certain wont drop within the day of holding time.  <response>: Its called day trading, and most people lose money at it. Often very large amounts of money. 