A person who knows Tao has a clear mind.

This is because he is able to accept contradiction and paradox in life, and see black in white. 

He knows that existence itself is a paradox. 

If there is no day, there is no night.  If no one is tall, no one can be short.  If there is no honor, there can be no evil.

Instead of expecting things to be always in his favor, he is able to see life in a stage of flux, and strike a balance in it. 

He seeks a balance in yin and yang.

Know the white,
yet keep to the black:
Be the pattern of the world.
Be the pattern of the world,
the virtue in you will endure
and return again to the infinity.

Lao Tze Tao Te Ching - 28