Once you've seen what can happen to the human body in a fight, the last thing that you want to do is get in a fight. Fighting because someone looks at you or your girlfriend wrong, or because someone walks in front of you, or bumps into you, is the most idiotic thing that you can do. The next time you feel the need to defend your honor, think about this.
Is it worth your life? You may think that you are the baddest man in the world, but you don't know if that guy has a knife or a gun on him.
Then if it is a "fair" fight, just you against him, are you ready to spend the next few years in jail for this? Things happen in fights that people are not ready for. The guy your fighting could fall and hit his head, you could get a very unlucky shot in, that causes serious injury or even death. Then you can live the rest of your life knowing that you took someone's life, all over something silly, like your pride.
The only time that you should resort to force is to defend yourself or others from actual physical harm. Even then, if it is possible, the best alternative is to walk away.