Although natural ability and genetics play a huge role in determining one's physique or performance, I still think the biggest indicator of success is a person's desire to succeed. There are many people who are successful in different areas of life who have no right being at the top of their profession if they were to rely exclusively on their natural abilities. They have become successful because they wanted the prize more than others and were willing to do those things that success in their field requires. Likewise, their are many talented and gifted people with amazing potential who never seem to succeed because they lack the motivation and desire to do so. Again, I think a fair question to ask is "who wants it most?"
I work with people all the time who tell me they are totally motivated and excited to change and they rate their motivation level at a 9 or 10, but talk is cheap and their actions show their true level of commitment. Sometimes it takes embarrassment, tragedy, or getting your butt kicked metaphorically, or literally to get to the point where we are finally motivated or scared enough to change. I prefer to focus on positive motivation as opposed to fear, but some people actually respond better to a negative stimulus. For some, it might take a doctor's lab results to wake them up to the reality that they need to start making some changes.
The fact that a person wants something more than others is what moves them to action. If they persist and fine tune their efforts, they can succeed. If you see someone with six pack abs, odds are they want that result more than most people who aren't wiling to have the disciplined diet required to get to single digit body fat. That goal isn't for everyone, but you should have specific goals related to your health and fitness.
Earlier this year I heard Erin Stern speak and she said the strongest force in the universe is the human will and if we can visualize, plan, and harness that power, then we can accomplish our goals. What is it that you really want? If it's something you think would be nice to accomplish someday, then you will probably never do it, but if you are serious about it and develop that burning desire, then you will probably pay the price that is necessary to achieve it.