Because when we experience fear, we hesitate, and when we hesitate, we question ourselves and require answers. There are many possible outcomes of hesitation, and one is inaction, to be frozen in fear. And if it is, in that space opened up by fear, you take responsibility for the action. You test your resolve that your destiny is to be no passive fact but an active factor. It means, in the words of a popular book-title, feel the fear and do it anyway.
Fear is a boundary-experience.
Growing people who push their own boundaries will always experience fear. Don't let it keep you from doing things. Let it alert you to the presence of a boundary. Let it signal you to hesitate, acknowledge the boundary and the risks, and embrace the act. Take responsibility for what you are about to do.