I may have a different opinion, but i believe that most times it is not about ego or greed when risk management fails.
Most times during trading, the market moves away from the predicted movement and does something entirely, which SL cannot stop, and it doesn't matter if you run a risk management plan or not.
it may be true but most traders of course wanted good returns during their trading, so they always predict in favour of them. they act according to what they thought will happen but its the other way around. if a trader will just be conservative with his calculations, he will not lose a lot of money, if in case he will lose that particular trade. but of course, the reality is different.
when you are already in the market, you suddenly change your decisions for the hope that you will get more money. i think thats where most failed, changing their strategies when they are already in the trading market.