Five Tenets: Self Control
Self control is not pulling your punches, self control is not punching - is a conceited thing to say.
Self control, like perseverance has a real physical aspect to it. All of the tenets impact on the real world through informing your feelings your thoughts and your behaviours, Self Control is simply the tenet with the most physicality because yes, being able to control yourself so your movements always have an appropriate amount of power is a really important part of what self-control is and what it is to be a martial artist.
As with all these tenets though, you can, and should go deeper. If self-control is about knowing the appropriate amount of force to apply in a situation, then it is also about knowing when to not apply force. Being able to judge a situation correctly is the other part of self-control and this comes from (when appropriate) having control over yourself and your emotions so that you keep making good decisions, even when you're under pressure, or tired or upset - as examples. This is where self control becomes an internal skill. Self-control is meaningless without the ability to judge the situation correctly. This means being able to identify what options you have available, and which one is the most appropriate to use. Just like in fighting you have a range of strikes, kicks, holds, throws, locks etc that you can employ, so to, before a situation becomes a physical fight, do you have options of how to behave. This feeds into self-defense theory which is not the focus of this post.
Self control will mean that you are able to deal with difficult situations without needing to resort to violence. This will make your life easier as there are very few situations where physical violence will be met without condemnation. This doesn't mean that there are not situations where violence in the interests of self-defense is not the option that should be taken - of course there are, but like I said, this is not a post about self-defense explicitly.
So self control is about not punching and it's about pulling your punches, and using all your power, and everything in between and beyond. Self control comes with experience and through the lens of the tenet of self-control that experience becomes a form of wisdom. In fact, all the tents provide lenses through which you can turn experience into wisdom.