In my opinion, when you one goal it becomes much easier to achieve that one goal namely because all of your energy is going into completing the one task at hand. As an artist, I believe that we struggle with this concept because we want to do everything creatively and are not always great at the "business" side of things. I am completely guilty of that haha. (That's why some people truly are GREAT at working in very intense businesses as opposed to working in the arts.) Everyone's different, and we can all learn from each other.
If you're a like me and great time with your creativity but tend to have a bit of a hard time "business-wise", set one goal that you want to accomplish and write it down. You will achieve it rather quickly, whether you believe me or not! Actors: let's say that your one goal is to book a national commercial. This now becomes the task that must be accomplished before anything else in your life! You then must tackle the task at hand! This includes researching every single commercial casting director, meeting them, finding a great commercial agent to help you, etc. It will be tough, but can do it. Start today and set your one goal, accomplish it, and move down your list! You will also tend to find that once you achieve that one goal, the others on your list become more and more attainable!
ANYONE can do ANYTHING that he or she puts their mind and spirit into. So, what's your goal? ;)