You take a picture of yourself and find that you have a bodypart that is not up to par with the rest of your body.
You start a diet to make gains, you train and you add mass.
You take another picture and say you added 20 pounds.
Now your lagging part is bigger, but so is everything else. You never really accomplished anything but get bigger. (which is great) But you want to bring up that lagging bodypart!
What can you do if anything, or do genetics just say, OK I will let muscles grow but only in proportion to what you have now?