This is called the main principle of Dao.

Fifteen

The virtue of the ancients made they who were scholars

subtle, mysterious, obscure, deep, and penetrating.

Their mysterious depths can not be understood.

Now : only because they can not be understood,

Therefore we try to emulate their appearance :

Hesitant!, as if crossing a winter stream.

Wary!, as if afraid of their neighbors all around.

Respectful!, they are like a visiting guest.