Imagine an hourglass.

Its shape is like the symbol for infinity. Its form recalls the double helix of DNA. Its two sections represent polarity. The material on one side, the immaterial on the other. The male on one side, and the female on the other. Hot and cold, positive and negative, or any other duality.

The sand runs in a stream, the same stream as the course of energy that runs up your spine, the same stream that is the road of life.

The movement of that sand is what we call Tao. Our consciousness alternates between the various states represented by the hourglass. It is as difficult to grasp as a stream of sand. Therefore, it is foolish to examine things minutely. It is unwise to focus on the material. It is wisdom to understand the movement.