Success is a byproduct of working extremely hard towards a goal. Working hard towards a goal, and never giving up, has a tremendous amount to do with BELIEVING that you can accomplish anything that you set your mind to.
It's not always easy to believe that things are going to work out, especially when you're faced with difficulty. It is understandable that you may be fearful! However, you must choose not to give into fear, and you must instead choose to "take the bull by the horns," and face your fears.
Remind yourself that you have the power to do anything that you want to do. Believe that you can and will reach your goals! Don't let anyone, (including yourself,) stop you!
I often advise my friends to "treat themselves like they would treat a friend." For example, if you're upset with yourself because of a particular choice you have made, and dealing with regret, don't beat yourself up! Or, if you're upset that you're sick, or not accomplishing all your goals in a timely manner, don't be hard on yourself. Treat yourself like a friend. You would never become angry at your friend for these things! You'd never say, "You should have known better," for example. Instead, you'd encourage your friend to keep moving forward! You'd also remind your friend that things always get better!
Be kind to yourself. And remind yourself, often, that things will always work out - even if you don't know exactly when they will work out. You just have to believe that they will. :)