Myth - You must stand still and balanced to hit every shot.
Truth - I do not stand still and balanced, and I have never seen a pro that does! Watch them on television as they hit, fall off balance, and recover. Pros do not stand still and pose like a statue after every shot. You should not either. This just does not make sense!
I am not sure where this notion came from, but I would forget it and let your body fall off balance after every shot until one day your balance improves while recovering. And it will!
Tennis is a moving game like riding a bicycle. You do not learn to balance yourself on a bicycle by staying balanced in one spot. Instead, you ride a little ways, fall off balance, then get up and do it again until one day your balance improves. The same is true for tennis. Move, hit your shot, and fall off balance to begin developing your balance on the move.
Leave standing still like a statue for pictures after you win the Wimbledon championships!