I am not sure actually because I learn it with a lot of failure, wasted a lot of time by believing those so called guru. But if you ask my opinion, the most hardest part to learn is psychology. On my view, profitable trading consist of 80% psychology and 20% of system. Let's take an example or we can even ask ourselves some of this question. A lot of people will said trend is my friend, but do they really wait until the trend is form? Secondly, do you always change your SL and close before TP? Thirdly, can you take small losses when you can read the chart that price action is against your trade? Those 3 are really basic psychology related, but the hardest part to learn. It is self-improvement and can be taught by nobody. I love to listen on webinar like Dr. Andrew Menaker, Randy Howell. When you listen to webinar, you will start to remind yourself and that's self-improvement.