This article by Jody hits the nail right on the head:
Everyone has a fear of something. It could be a physical thing like spiders. It could be a fear with no known reason, like a fear of heights. I have a friend who is terrified of elevators and another whose worst fear is not being able to protect her child. These fears range from something that perhaps could be confronted with a lot of bravery and courage, to phobias so intense they literally control your life.