The fear that some feel and others don't is just a different perception of the same experience. If you perceive yourself to be less than you are, believing that you're "not good enough", so keep telling yourself, "I can't do this", "what if they don't like me", "what if I forget what I'm saying" "what if I trip over or faint", "what if they laugh?", then your body and subconscious mind will seek to actualize that reality for you. It will sabotage your conscious hopes to do a thing well because it is running on a contradictory belief.