Most traders always think that acquiring the skill of trading will reduce the losses,yeah it's right a trader knows the fundamental and technical analysis of trading.But a greedy trader may end up with losses most times for instance a trader targeting a profit of 100% and when the profit is 50% he/she won't sell the current profit and when the price drops the trader regrets and loss.And also a trader should trade an amount he/she can afford to lose in order to reduce great loss.
That's the problem with such kind of a trader, if you are more on your emotions you will be dominated by greed and fears, though some may develop good attitude with that basic principles, as long as you can handle the pressure and you know how to move forward if in case that you failed your attempts.
Your mentality needs to be driven by facts and knowledge regarding to the business that you are into, if you failed to control yourself then that's the time that you are endangering your deposit.
Decision making needs to be based from the knowledge and understanding and not by emotions.