"'Being watchful over oneself while alone' is to have a mind which is watchful over its own knowing. It is the same whether one is with others or by oneself. Even when one is with others, one's private thoughts are not known by others. When pursuing the solitary knowledge of one's mind, there are no external restrictions. Having no depraved thoughts, allowing no self-deception, making the will sincere - this is the meaning of 'being watchful over oneself while alone.' When a thought arises in one's mind, one spontaneously knows if it is good or evil-this is knowing. Knowing is the spiritual intelligence of the mind. It is originally without good or evil. Thus it illumines good and evil. It is like the mouth not having the five flavors, yet being able to distinguish them; or like the ear not having the five sounds and yet able to distinguish them. To take solitary knowledge as one's ruler and to watch over it - this is the meaning of honoring the virtuous nature."