The pros master each shot off the court and then react naturally on the court. Is it a mystery? No, that’s what you need to do as well. Master your shots so well that they happen like a reflex.
Have you ever tried to think about walking? As soon as you think about it–you change the way you walk and it feels unnatural. And yet, you probably mastered walking years ago!
The same is true with tennis. Once you have mastered a shot, the more you think about it, the more unnatural it will be. But until you master it, you will continue to expend more energy than you have to, without the results you want.