In trading you need to gain knowledge those learnings you've got will now execute your trades every trades you made you learn and earn experience, if you win great those learnings applied but if you fail learn from those mistakes, analyze whats wrong with your trades, prevent to deal with again and move forward for your future trades.
One of the biggest problems of a trader is repeating the same mistakes, it seems to me that this deprives the trader of the opportunity to become successful. I'm pretty sure that everyone who found themselves in a difficult situation and did not use a stop loss thought that it could save them money and time, but if after that the trader continues to repeat this mistake and does not use a stop loss in future transactions, then this leads to the same result again.
That is the reason professional traders keep a notebook with them and keep track of their bad trades. They try to figure out what went wrong and how he could be saved from that. This is a good practice for a trader, as it helps him identify the same scenario in the future and take action according to his previous experience. Not sure how much it help them but there must be some benifits of it otherwise why most of them suggest to do something like this to newbie.