In my very limited experience, fear seems to have a stomach. The more you pay attention to it, reflect about it and hesitate, the more you feed the fear, the more able it is to incapacitate you.
The strongest weapon against it is to take away the feeding mechanism. Acting impulsively, before a single thought can enter your mind. Fear is irrational but you rationally feed the fear, so acting irrationally, entirely impulsively, will defeat it always. Some people do have a tremendous amount of trouble being spontaneous thought, gladly I don't.
In other words, like some guy working for Nike said it much better than I could : Just fucking do it.