Fear is a protective emotion, without which the human animal would not have survived - early man would have walked off cliffs, walked into the mouths of hungry predators, and followed their curiosity about poisonous snakes.
But in an intelligent, conscious species fear can get the upper hand so that one's life is dictated by fear, as the imagination places possibilities before one, and consequences that may never come about. You have a saying - burnt once, twice shy - meaning that the fear can outweigh the original incident, growing in significance in memory beyond what it was in fact. A common situation is a crippling fear based on a childhood incident, blown all out of proportion due to the child's perspective. He was tiny, got yelled at by someone big who theoretically could kill him, crush him like a bug. Now an adult, the grown child finds he cannot bear to step into a similar situation, as he feels an overwhelming fear, a sense of impending doom, that he is about to be killed. Perhaps the original incident was over a cookie, but the adult translates this into any object desired. Thus, the adult is crippled, unable to pursue a job opportunity or ask for a date or purchase a new car - all because he got yelled at once when reaching for a cookie.
For those who think this example extreme, it is more common than not. Fear, in an intelligent species, can be an unreasonable fear, and when allowed to become thus is dictating the person's life. The key to freeing oneself from such strictures is to examine the reasonableness of one's fears. What's the worse that can happen? If you make the move, will you truly be killed? This examination separates the fear of walking off a cliff from the fear of asking for a date or wearing a different style of clothing. After having determined that a fear is unreasonable, without a valid basis, then ignore it and proceed. The fastest way to dispel a baseless fear is to challenge it.