so, i've been taught over the past few years of tennis lessons that my groundstroke swing is a 2-step process. after my lower body is in the right position and i've turned my upper body back, i need to turn my shoulders forward first, then my lower body. shoulder turn should be up to just before contact, then lower body takes over after that. basic stuff and in most situations i can execute it but really fast balls screw me up. my instructor says when i return fast balls, i get into position properly but end up just hitting with my legs without first turning my shoulders. it drives him crazy. i feel like i don't have time (lol, that's the excuse for everything, right?!) and for fast balls, i'm just happy to return them. but, how to fix this? i know, shorter backswing. any other tips to get my mind in the right place? when i learned it the first time i used to count 1 - 2 so i'd know when to switch from shoulders to legs and that helped ingrain it in my head. but for really fast balls i don't have time to count, let alone think. i'm just reacting. i also don't quite get why it's so important. is it because i need to be hitting the ball in front? or because i need my arm out in front to generate the most power?