In the beginning of one's training, the mind is fully occupied with learning how to move the body correctly with individual and sequenced movements. There is no extra mind-space for daydreaming or maintaining our habituated internal dialogue. At the intermediate and advanced levels, the mind should be applied towards attention and intention. Here there is difficulty however. The body can now move itself with only a little intention, leaving the opportunity for the mind to wander without the mind's attention.
Intention can never fully develop.
The chi can only be activated by using one's attention to discover what is at first only a very subtle feeling. Intention requires that the mind be fully and completely engaged in each individual movement as well as the flow of movements. As one progresses, there is more and more to be discovered in the feeling and flavor of each movement. Always be attentive to the inside of the body as well as the outside of the body. Let the body and the mind become one.