Your genetics are the last and final word on how big you will be and how you look. you think Phil heath or Lee Priest haven't tried every fucking routine there is to improve their pecs?...and yet they both still have sub-par chests, even after years of pro-level cycles.
this goes for EVERYONE. if you are a skinny tit with zero muscle, odds are you will remain a skinny tit no matter what you do
genetics does play a huge role but is definetly not the final word. you can take a so called genetic freak and make him train like shit and eat candys and carbs all day, he will never sport a six pack, ever.
I know guys that have have excellent physiques naturally and all of them bust their asses off at the gym and are paranoid, almost psychopath, about their diets. Have never met or hear about those genetic gods that trained average and ate average while sporting a 200lb ripped phsyque, not even close do that.
In a nutshefll, if you have bad genetics no matter what you do or eat you will look always way bellow average. If you have good genetics you have the potencial but you still have to train and eat like a mofo. There is no free lunch either way. I REPEAT, NO SUCH THING AS GENECTIC GODS.