You can succeed. You have the right stuff. The seeds of greatness reside deep inside you; all that's required is for you to water them with dreams and effort.
Why is it so difficult for people to believe great things for themselves? Do they really think other people (the ones succeeding in life and living their dreams) are really that much better? Do they believe in luck or chance?
The successful simply had the audacity to mount a pursuit of their dreams. They had the guts to try, the tenacity to stick with it, and the stubbornness not to quit.
Perhaps you need to consider the fear of regret that will result if you don't make the attempt. Maybe you will find that fear to be stronger than the one holding you back. Your dream life is available for the taking. What are you waiting for?