1.Fear of losing,this is the one among of the factor which influence many people to do wrogh in stock market, is when price of stock go down ,fear influence these people to stay out of the market,and when stock going higher most of the they posses FOMO.
2.Lack of enough education,for most people lose tons of money due to lack of knowledge about investment which they choosen to invest.
3.Lack of good stock infrastruture,i remember in 2017,i invested in bitcoin but,i bought locally ,without any live btc price chart,so i bought with bad price ,due to that i lost all of my money,but this is due to lack infrastructure back the time.
If you have anymore reason please share with me,i will thanks u.