I was asked recently by a student 'how do you fight a big guy?' Well I had to ask 'why would you want to?' and then 'what are you doing that you are risking having to fight someone?' Martial arts study is not about being able to fight people, martial arts is about NOT fighting people. Martial arts is about courtesy, respect & humility not proving you can beat someone in a fight.
If we are humble, courteous and respectful the need to use our fighting skills should rarely ever arise. If you are nice to people they are less likely to punch your face in, or want to. Of course there are those who are predisposed to violence but in the main they can be avoided by frequenting places where they don't go.
Martial arts is about communication. Martial arts study helps us to understand ourselves. If we lack confidence then martial arts will help to alleviate that. If we lack self esteem martial arts will cure that too. Both of these examples; confidence and self esteem are communicated through behaviour and body language. Low self esteem is easy to see in a person and the study of martial arts builds confidence and self respect, not in a 'look at me, I'm so tough' sort of way because that is not real confidence that is bravado which seldom is the same inside as out. No, martial arts builds a quiet confidence based on personal achievement and progress. Progress through repetition, the belt ranks, and a supportive instructor will build a strong foundation of self belief - And, deep inside one has the knowledge of how to use physical martial arts if one has to. It is built into the muscle memory, a knowledge that permeates ones entire being and this is reflected in how a martial artist moves and behaves. Martial arts develops a neutral body language that is neither threatened or threatening. A body language that just 'is'.
Sustained study of the martial arts alters our whole perception of 'self' gradually stripping away our insecurities and fears and replacing them with a solid foundation of personal worth. Training with other like minded people creates friendships based on shared goals without ego or bravado, instead a simple state of being. This is the communication of the martial artist. I have no wish to fight, I do not see life as a fight either, I don't act tough and the other martial artists I know are the same. If they are not they are probably a beginner and the need to act tough will pass in time.
If you are studying martial arts but still lack confidence or self esteem then I would say this: It's normal for us all to sometimes doubt ourselves and our own worth. But these feelings are just remnants of a previous life, they are the past and only as real as we choose to make them. Our skill as a martial artists is to know that we are not our pasts, how tough we are is entirely relative. Someone is always tougher or weaker, more intelligent or less, better educated or less educated, richer or poorer. Whatever they are does not affect you unless you decide it does. Focus on training diligently and thoughtfully and you will come to realise this in your own time, don't force it, instead enjoy the journey, treasure every step of the way and confidence won't matter anymore