Self control
Who controls your actions?
All persons can get mad if somebody just pushes the wrong buttons on us. The person who responds violently without thinking of their actions has no control over himself and will face the consequences only  after when it's too late to regret them. But the person who takes a moment to think will take the best reaction conscientious of the consequences.  
The way we respond with controlled anger or with violence shows our level of self control. Karate teaches us the way to master ourselves by keeping calm even when we are in danger.  We don't allow anybody to have control over us.
Mastering me
You can be the master of yourself by training your mind and your spirit in the way that you will react according to YOU and not to your ego. Your ego is the one hurt when somebody provokes you.  The higher your ego is, the higher the provocation hurts you.  If you destroy your ego to be yourself you will master your actions and you will be free erroneous actions.  Karate-do is the way to master your own self.
The army general
Think of you as an army general that engages into an action that can take his troops to the victory or to death.  A general who does not have self control  will not evaluate the consequences and  possibilities to be defeated and will put himself on the brink of ruin.  

You are the general of yourself only if you have command over your ego.  In karate  is the same thing, if you act with anger you will  loose the fight.  Karate-do helps you to have self control and to  act as a  general that will think of  the results before to engage into a conflict.  Walking away from defeat is walking trough victory.