Competition is good, but you should play sports because you love them and not just to win. But if you both love a sport and really want to win, is hard work all you need? No, depending on your genes and your sport of choice you may be at a major disadvantage.

It all comes down to body size, and whether or not yours lines up with what you're asking your body to do. Swimming? You want to be bigger. Running? You want to be smaller. And it's not just about weight, either, your height plays a big part -- and all dieting aside there's no way to change how tall you are and your basic physical traits.