They understands that it does no good to become stressed and panic, in fact, they knows that by allowing their mind to become stressed is defeating oneself within one core.
You have to be able to control your mind and think rationally during times of duress; you cannot panic or let your fears take over.
This is easy for me to say while I am sitting behind a desk and writing in the comfort and safety of my own home, but how do you control your mind and remain calm and collected when you are confronted by a knife wielding thug in a parking lot?
The answer is that you have to practice controlling your mind and emotions, before that situation ever arises.
You must put yourself into these kinds of stressful situations during your normal practice sessions.
Realistic practice scenarios prepare your mind and body to deal with that rush of adrenaline that you will experience if you ever find yourself in such a situation.
Dealing with these emergency situations is just like dealing with any other situation, the more experience you have, the better equipped you are to deal with the problem.
This principle applies to everything in life.
You become better at things as you do them, whether it is playing the piano or dealing with a violent encounter.
ps/smoh
