“Bravery is being the only one who knows you’re afraid.” – Colonel David Hackworth
Fear is a feedback mechanism from the environment to our body and brain of potential (or actual) danger. Since we are all human and subject to the same external stimuli in the same circumstances, we all get scared in certain situations because it is our survival instincts kicking in.
But when you are cool on the outside, when your calm is contagious and carries over to others, even if you are in turmoil within but still keep it under control and do what is needed, others will call you brave. If you are trembling inside but you go forward in spite of the fear, you are brave.