I think it comes down to bone structure, the ammount of androgen receptors you have also known as how well you respond to steroids, side effect tollerance, doing it for years on end, and most importantly going to the gym relegiously and putting 100% effort into every rep. Also these guys spend all of theyre money on bodybuilding they eat all the food possible they have perfect diets usually and alot of them have ways of making large amounts of money the normal person is not willing to do so they have more money to spend on food, steroids, supplements, chiropractors and all of that stuff. But really how many people do you see who use gear for about 8 years strait who even have good genetics not many people can handle that. I think that if you are a normal guy you have the ability to go pro you just have to have a un-normal amount of dedication to reach your goals and be willing to sacrafice everything.