As with most issues of mind/matter in human endeavor, cause-effect isn't always a one way door.
Per NLP, people have a tendency to look up and left when they're making up a visual image they haven't actually experienced. Imagining an image or scene CAUSES the eyes to drift up that way. But the flip side is that if you WANT to imagine with greater visual clarity, you can look up and to the left first, and the results will tend to flow much more easily.
Tennis-wise, people spend a lifetime trying to find that zone that allows them to play with subconsciously perfect footwork and ease of movement. I blame Timothy Gallwey. The discovery by psychologists that cause-effect is a two way door has caused a lot more problems than it has cured. When it comes to the mind-body connection, it SOUNDS a lot friendlier to skip the somatic beatings and go straight for the esoteric luxury of the mind. You get to skip all that unsightly and difficult building up of sweat equity that way. But in practice, *successful* mental training is often far more grueling and time-consuming than its meat counterpart. The far more efficient method of entwining those three things -- fitness, footwork, and "the zone of effortlessness" -- is to work on the first two. Then, that "zone" comes more and more frequently and easily, like magic. It's why there are successful academies dedicated to training the physical process that are churning out pros, while the process that begins with the mind is a lot more likely to appeal to the couch-bound housewife and hit the top of the bestseller lists.
Most magic comes a lot easier if you put in the work, first.
You want a bullet-proof on-court mind? Treadmill and Spanish X drills to you puke. When it's easy to get to every ball, most of your doubts evaporate. "Mastering the mental game," is by and large snake oil.