When you realize what it is, take an action that is diametrically opposed to that which you fear. This will confront and conquer the fear by giving you the first step in the right direction. Quite frankly, what keeps most people from success is that they simply don't have the energy, or make the energy, to do what it takes to move to the next level. Lack of perseverance. Oftentimes the race is lost because the race is not finished.
Success is often just around the sharpest corner or the steepest hill.
One more hill. The saying is that you can achieve what you believe. Ask yourself what kinds of beliefs you hold. If you don't believe that you can achieve than you won't. Your pessimism will prove yourself right every time.