Their worst mistake can turn out to be following someone without any track record. When an unskilled trader sees another unskilled trader sending some filled images with so many indicators and boxes saying this is high and this is low, take your trades here - and then he takes the trades personally and loses, he also lose trust on others and lose hope in crypto. In copytrading also, it is not good to follow anybody based on their recent past performance but their overall results.
People often think that someone who has already been trading will be able to make better trades than them, and they think this way without even trying themselves and learning much about trading or the market. Some are lazy and some are simply in a hurry to earn money so they skip the learning part and think that they should start earning profits immediately after entering the market which is a wrong mindset to have since things can go very wrong sometimes.
Yes just by seeing that other people who have traded they think that that person will be able to be better in the next trade, but I don't think it will always be like that, because they only "have" traded not someone who is actively always doing that. So maybe they shouldn't make too many assumptions without knowing what the real difficulties are in this trading world and of course maybe the other person they think is better is actually far below them, meaning they are much worse at trading than you, it could be. True, not everyone is a good learner and of course there are some who struggle with learning, it depends on themselves, but for those who are lazy learners I don't think I would blame anyone else but themselves. Of course, this happens for several reasons, as you mentioned, it is not uncommon for those who are in a hurry to enter real trading but are still very low in terms of knowledge, they are too focused on profits but do not pay attention at all to preparing to minimize losses, and yes, in the end, instead of profits obtained but losses even more dominate.
It is much better for a person who wants to venture into cryptocurrency trading to learn the essentials about trading and the cryptocurrency market and practice using demo accounts to check their skills and then start trading themselves, with a small amount initially so that they don't lose a lot of money in case they make a mistake. After some time, they will be able to trade effectively.
Basically trading is very risky because the nature of the market is very volatile and anyone will not be able to predict with 100% accuracy, even those who are experienced still have difficulty. Losses will always be there, and I am sure you will not want to continue to experience losses, well so the only way to reduce the amount of loss is to learn a lot about something that can make you lose and avoid it. So you will be able to get profits consistently but with a lower level of loss because you always learn to be better.