Windows and doors are cut into a wall. It is their emptiness that makes the windows and doors useful.

                                                                       -Lao Tzu

In ancient China, the keeper of the Imperial Library, Lao Tzu, was famous for his wisdom. Perceiving the growing corruption of the government, he left for the countryside. On his way, the guard at the city gates asked Lao Tzu to write out the essence of his understanding to benefit future generations. Lao Tzu wrote the Tao Te Ching, left, and was never heard of again.

The Tao Te Ching (also called "The Tao"), by Lao Tzu, one of the most influential books in history.  It is the source of famous Chinese sayings such as "Those who know do not speak, those who speak, do not know" and "Even a 1,000 mile journey starts with a single step". The above quote comes from the Tao.