I think most investors often lose money because of fear particularly it happens to new investors.like take coins investors as example. They always sell their coins when the market is going down or the particular coin they invest in is dumping.but they don't know that is not the right time to sell but few losses because they invest all their money  and anytime they have financial problem go there to sell some of coin they invest in,and some people don't have target and anything you are doing once you don't have target that means you are also ready to fail, always try to have target.