Someone on quora asked:
Fear is an instinct, to keep one away from danger.
Sometimes the fear is valid. Such fear can keep you alive, especially in crisis situations. Examples are fear of falling or fear of injury.
Many other times, fear is simply a vestige of our prehistoric brains not yet adapted to modern times. An example is fear of humiliation, maybe manifesting as a fear of public speaking. Our prehistoric lizard brains are afraid that we might say something stupid and be humiliated and lose standing among the tribe, leading to us being ostracized. In prehistoric times, being ostracized can mean death, since humans had to band together to survive. But in modern times, such fear is unnecessary and unhealthy since people are more free to disagree with one another.
The key is to recognize fear for what it is and to understand whether the fear you are feeling is justified and needs to be acted upon, or simply part of a prehistoric instinct that is meaningless in the modern life.