As such depending on the reason of their failure the actions needed to correct those outcomes will be different, however taking into account what I see in the forum with those which are newbies, I really think the majority of them do in fact lose their money due to a lack of understanding about the markets, as they believe they can make a lot of money without the need to invest their time and effort to understand what trading is really about.
I agree to this because greed is a major problem not only for newbie trader but for the trader who thinks he is experienced. If a trader of any standard get greedy, he will be tempted to chase profit and leave out the important trading strategy which will guide them. This is a serious thing for traders, greed makes a trader to increase leverage and sometimes trade in martingale style.