of course traders must learn from the mistakes they have made, it is very difficult, but it can make you more confident, and indeed it takes time to get up, if you don't want to lose your money too much, use small capital, your emotions will surely will be controlled 
Some mistakes will happen again if we don't take it seriously and sometimes a small mistakes/decisions will lead us to a big problem. Confident on trading will come to you if we already knew every detail, strategies and analyze in the markets. There are many strategies you can do to make profit in trading and all you have to do is find the best strategy that you can easily do then find other strategy that can may help you more in other trading. I believe that everything will be in proper order in the right time of trading. We must trust the process of learning every day. As long as we can learn from the mistake, and we can prevent from making the same mistake, we can recover what we lost. Sometimes, when we make a profit, we will feel confident, and for some people, that confidence will become bigger and makes them overconfident. So you need to stay calm in any situations even if you are making a big profit. Yes, I agree that with learning about the strategy, you will have a chance to make a profit, so you need to apply every strategy with the current situations, and make sure to know when the right time to trade.