What is self?
It is explained that when we look at a mirror we do not see its actual surface. We do not see the actual mirror, only the images reflected on its surface, which appear as reality. Likewise, mind or consciousness is like a mirror. In it we see the images of physical existence and life experience, which we take to be the only reality. But the Yogi asks himself, what is this that is conscious of all these images? What is this mirror we call consciousness? Who am I?"
We don't posess the necessary senses to properly answer that question. If you can't see the mirror, you can't answer the question "what is a mirror"... you can only infer from what you can see that a mirror reflects. And really that's all we do is infer from what our senses tell us.