Whenever you are exposed to long term abuse, in order to minimize the external damage you will have the tendency to control your behavior in order to please your abusers to avoid the negative consequences of displeasing him. But not because you particularly care about his well being, but because if you don't match his requirements he will punish you.
For example: if a slave gets whipped whenever he spills wine, he is going to try very hard to don't spill wine to avoid being whipped.
For as long as you are trapped in that situation, self control is a great strategy that will reduce the amount of external abuse you will receive. If you manage to escape that situation and you continue to control yourself in any way, that is what we call mental illness. This is why symptoms sometimes persist even after the abuse stops, and a significant period of grief has past.
There is not such ting as good authority, whenever someone becomes the authority that person is exercising acts of evil. Whenever you have authority you end up with the master and slave dynamic.
Because you were abused in the past, you were forced to become authority, you are abusing yourself today and sometime other people around you ass well.
There is a huge distrust in allowing you to do whatever you want because of, struggle and perhaps poor decisions in the past, that is motivating you to control yourself.
However this is how things where meant to be under normal circumstances. Whenever you allow people to have autonomy they follow self preservation.
The problem with self preservation is that: things that are good for you in the short term, might be very bad for you in the long term, or might be bad for others. This is why nature built in two insurance policies called: free-will and self defense.
Free will is the ability to learn from consequences and avoid negative consequences, and when free wills fails to prevent someone to avoid negative consequences you can stop him from subjecting you to that abuse by defending yourself.
Self mastery is basically the same game as an external master, you still end up with a master slave dynamic only that you are playing both roles. All control is evil, including self control.
I am not saying that it is bad to become very good at something, for as long as it is pursued voluntarily.