There is one thing that can stop a dream before it starts; non-action. You can say you believe in your dreams but never take action towards reaching them. When you don't act on your dreams, you forget about them. Life happens and as reality sets in you have no time to dream. The life you want may be a fantasy, it may seem impossible but what is wrong with that? What is wrong with having a dream so big that it scares you? It is okay to be scared as long as you don't let fear stop you from action. Your actions reinforce your beliefs.
You are more than able to reach your dreams. More importantly you can live the dream now. Your actions now may seem insignificant but they are purposeful. They shape your life and prepare you for where you are going. Keep believing in yourself. No matter how hard the journey may see, you are worth it. Your life matters. Your dreams matter go live them out.