One major thing I know can't be taught is the psychological aspect of trading.
Control emotions is one of the psychological actions in trading that is hard to follow and manage. It is very easy to say and advise to some trader to manage their emotions but it is really hard to implement in real life.
But we have different goals in trading that will give us the reason to move forward and to become a better trader. We also have different trading styles, different lessons learned but we should always stick to those positive things.