This kind of thing is very important in traditional martial arts. But this is not necessarily a very mysterious thing. Repost an earlier reply about the usefulness of Wushu psychology;
Wushu psychology is a conscious activity when practicing Wushu. China Wushu, no matter what genre, has its own practices, usages and methods. All three are considered as China Wushu. This is also the difference between traditional Wushu and modern Sanda.
For example, if you lift a bucket of water, when you know how much water is in it, you will lift it with corresponding strength. But if you carry an empty bucket and always think that bucket is full of water, what effect will it have? You will at least hold the bucket high at once, and you may even lose your center of gravity. This is the role of the heart. This is the principle of Wushu psychology.
Xingyiquan and Heart Liuhe Boxing are both introduced in this way. When practicing every boxing, try to keep your mind a little longer and farther. When practicing, you should feel that an opponent in front of you has been played by you and will fly far away. In the long run, you can make your body relax and your strength become smooth.
Of course, the above is just an example. What I'm talking about is just a common mental method. When you study deeply, you will practice boxing in other ways. Even contrary to the above. This is not surprising. Each method has a different function, and the things you practice are different.
If you are practicing martial arts, it is easy to find the mental method, that is, those conscious activities about boxing in the boxing spectrum. This is the way to practice boxing.
Yijinjing and pulp washing are both advanced things. It's no use reading them if you don't get there.