Most people buy a stock because they hope it will go up and they will make profits. They buy on tips, or what someone else thinks, without any concrete knowledge of their own that the stock will advance.
Thus they entered the market wrong and did not recognize this mistake or attempt to correct it until too late.
Finally they sell because they fear the stock will go lower and often they sell out near low levels, getting out at the wrong time, making two mistakes, getting in the market at the wrong time and getting out at the wrong time. One mistake could have been prevented: they could have gotten out right after getting in wrong. They do not realize that operating in Stocks and Commodities is a business or a profession, the same as engineering or the medical profession.