I think the most fundamental reason a trader fails is the lack of knowledge and experience about trading practices and the market. They don't know how trading is done, they don't have any knowledge about trading strategies, indicators, or anything else that might be important for a trader to know before they get financially involved, and even if someone has done some research and gained some knowledge, they haven't practiced what they've learned.
So, a trader must first gain knowledge, enough knowledge so that they don't get confused at any point in their journey, and once they do that, they should practice that knowledge using demo accounts applying all the indicators and strategies that they want to use in their trading when they start with real money.
Most people who experience failure in trading do not have good knowledge of the trading they do and they do it not with the skills and knowledge they have and they do it based on how they feel when they see people who have been successful in trading. There's nothing wrong with using a demo account to try with the knowledge we already have, but trading with the capital we have will certainly not be the same as using a demo account. It's important for those of us who want to trade to have good knowledge in the field of trading we do.
That's the importance of understanding and experience even if it's just a basic understanding of trading but it's good enough especially for beginners who are just getting involved. Failure is normal, but I wouldn't exactly say it's normal if you come in unprepared with what should be prepared in general like some basic things when someone wants to get involved in trading. I think before you go in you should have done some research and found out about what you should be prepared for, but that's not always possible, because obviously like you said and it's not uncommon that lately a lot of beginners come in just because they're too focused or tempted by the profits that other people have made and with that they don't think about other things like some of the preparations that a beginner trader should have, one of which is good planning, management and some risk management.
Honestly with that alone I can already confirm what impact they will feel later, failure with a considerable level of loss is very likely to occur when you come without bringing any fishing gear, yes I understand there is a great profit opportunity there but you must understand that it is only an opportunity and it is not easy to get the benefits that others get. Therefore, that is why we must have the right understanding along with some qualified preparations, because none other than all that will be able to lead us to a profit, and to minimize the risk of loss then you must have very good risk management in order to avoid the amount of unexpected losses. There is no certain profit but by making everything run in balance then you will be able to make the profit come for sure and consistently.
And yes that's right, honestly I also started like that, when I first entered the world of trading I always used a demo account as one of the stages of learning and understanding, I did not immediately start on a live account because I clearly understood all the risks that could occur in the midst of my limited understanding, the account was one of the best alternatives for anyone, as long as they could learn and utilize it properly, and over time if you feel you understand enough then you can start with a live account.