Genetics is a HUGE factor, every pro bodybuilder has great genetics, just like every pro football player does. Now obviously it takes drive and determination, but you cannot obtain a pro physique without good genetics.
Everyone can improve on their physique, but only as far as your genetic potential will allow, that is all I meant.
Many people think that if they had all of the drugs that the pros have they could be a pro bodybuilder too, unfortunately that is not true. Just the same not everyone can be a star quarterback on the NFL, it takes a combination of genetics and the determination to utilize those genetics to their fullest potential.