The answer to that is pretty simple. There are a myriad of movies, documentaries, and books centred on people that have had a dream and then achieved their goals. So, what is the common denominator of those that achieve their dreams?
All the achievers have an absolute belief in themselves and a belief in their goals based on who they are and the world in which they live. Even those that fight the system to break through understand what the system is they must beat. They all have a goal that is completely aligned with their values.
That means that to get that same belief in yourself and your goals you need to first understand the environment in which you are working. You need to understand yourself and you need to have a clear understanding of your values. When all that is aligned you can become wedded to your goals.
Be assured that their will be plenty of tough times, plenty of times it appears the world is against you and plenty of times you will think Murphy was an optimist. It is at these times you need to have a binding commitment to your goals imbedded in your beliefs and values.
The starting point to all this requires hard and sometimes boring work, which is why most people do not bother.