It is not only what your genetics are like if your aim is to turn pro or how hard you train or your consistency, it is also very important how your body reacts to all the different kinds of drugs you are ingesting for years and years. Not only the positive, anabolic effects but also the negative effects, the side effects.
You need to have a constitution like a horse. For example if Ronnie Coleman and now Jay Cutler didn't have constitutions of a horse they would have been sick a long time ago and wouldn't be able to actually continue competing like they are competing. —Nasser