The Witness is that which is capable of observing the flow of what is—without interfering with it, commenting on it, or in any way manipulating it. The Witness simply observes the stream of events both inside and outside the mind-body in a creatively detached fashion, since, in fact, the Witness is not exclusively identified with either. In other words, when you realize that your mind and your body can be perceived objectively, you spontaneously realize that they cannot constitute a real subjective self. As Huang Po put it, "Let me remind you, the perceived cannot perceive."
An old Rabbi once asked the pupils how they could tell when night had ended and day had begun.
"Could it be," asked one of the students, "When you can see an animal in the distance and tell whether it is a sheep or a dog?"
"No," answered the Rabbi.
Another asked, "Is it when you can look at a tree in the distance and tell whether it's a fig tree or a peach tree?"
”No," answered the Rabbi.
"Then when is it?" the pupils demanded.
"It is when you can look on the face of any man or woman and see that it is your sister or brother. Because if you cannot see this, it is still night."