TAO is Non-TAO (non-human)

"To know that you do not know is the best.

To pretend to know when you do not know is a disease.

Only when one recognizes this disease as a disease can one be free from the disease.

The sage is free from the disease.

Because he recognizes this disease to be disease, he is free from it." 

(Tao Te Ching, 71)

From here, as what Wing Tsit Chan commented, we can see that such Taoist notion is quite similar to that of the Confucian "say when you know; don't say when you do not". However, we must also see that it is just a "quite", and not a total parallelism. We must remember that knowledge, from the Taoist's perspective (in respect to the idea that knowledge and desires are dangerous), is a "disease", therefore there is no way one can be considered right when he/she will "say when he/she actually knows". 

Somehow, someway, it just vindicates the idea of the Taoist Tao to be something that is not to be associated only with the human beings; for it is something that doesn't consider anyone or anything to be preferred upon. In other words, it flows in everything and every beings, and therefore must not be of mere humanistic foundation/basis. Yes, it flows within us, but it also flows in others; not only to other human beings, but also to other things; all the things that there is.

Now, to consider that the Tao is to be grasped by, or even to be known by the human beings themselves destroys the essence of the Tao as something that is impartial and whole-accepting "is". And since the sage, or the philosopher, knows (like Socrates) that he/she cannot know anything that is ought to be known, and only that "is", which is the Tao, is the only one who/which knows what is then ought to be known. Thus, it is not the "knowledge" which is the disease, but rather the unstable humanistic one (knowledge) which is incorporated to that of the human beings who are limited and are open to imperfections and mistakes. The knowledge of the Tao, on the other hand, is not a disease.

As a consequence to such assertion above though, people then can see knowledge, and the effort to have such, as something to be useless, because no matter what knowledge it is, or how it was formulated, once it is from the human beings, according to the Taoist point, is not assured to be a genuine knowledge at all.