The world is not enough for those who strive for greatness. They see the world through a different lens than the rest of us. They see the constant challenges ahead, and try to meet them head on, so they can go on to the next thing that stands in their way. Looking to attack the world versus waiting for the world to come to them.
With that comes a degree of discipline that most of us may never find. Without discipline, then you truly can never reach any goal because discipline is what guides you through the process. True, there are potential physical or mental aspects that will prevent you from reaching certain goals. However, aside from that, it comes down to your ability to block out the world and focus on your passion.
Learn to be disciplined in your passion, and you will find that excelling will come easier.