Because one's self-consciousness

or ego-consciousness is too conspicuously present over the entire range of his attention, it interferes with his free display of whatever proficiency he has so fat acquired or is going to acquire. One should remove this obtruding self or ego-consciousness and apply himself to the work to be done as if nothing particular were taking place at the moment.

To be of no-mind means to assume the everyday mind.

The mind must be wide open to function freely in thought. A limited mind cannot think freely.