Tweetalot imo has to do with genetics,some body parts arent as good as others . Some grow better then others do. sometimes no matter how hard you try it just wont grow like you want it to. Welcome to our bodies.You might want to see huge resiluts when you actual wont and you have to take what comes to you. Sure I wish my arms were bigger and ive done alot of different exercises for biceps but I take what I get