Control, regret, courage and a lot more.
These are emotions that burst out whenever you decide to sell or buy.
If you can manage to get the best out of all that then maybe you can succeed.
Every traders are different and I agree we all have different level of these things, perhaps not any have the control, or courage to trade but then that's not the case. If we are able to trade with less emotion, we can have a success ending but you can't just tell people to trade with less or no emotion at all coz we are playing differently, you can't be emotionless with the money you work hard after an 8 hour shift to trade and risk to the market. What I want to tell is, we are all different maybe some strategies are not as effective as they way you do it than the others.
It is true it cannot be learned in any tutorial out there.
What you need is experience by doing it over and over again.
What I think of a thing that can't be taught is the experience, we all lose, we all win, yes but it has differences a lot of differences.