Fear: be afraid or feel anxious or apprehensive about a possible or probable situation or event;
Everyone has a secret fear of something, whether it be rational or not. Sometimes, there is cause for your fear, but commonly enough, your fear is irrational. You may have a fear of being left by someone you really trusted. You fear it so much, you don't put trust into anyone, and you keep people shut off. But eventually people will get tired of pushing into a brick wall, and will leave you. A self-fulfilling prophecy.
While fear can be an amazing motivator, being swallowed whole by your fear can cause restrictions in your life, and can often times lead you directly to your fear. But if you can understand you fear, and accept it, while trying to work on it, the chances of a more successful life are far greater.
Because in the end, "that which does not kill us, makes us stronger" -Friedrich Nietzsche