Imagine you are sitting in front of a glass door that leads out into your garden, looking through it, gazing out into space. It seems as though there is nothing between you and the sky, because you cannot see the surface of the glass. You would bang your nose if you got up and tried to walk through, thinking it wasn’t there. But if you touch it you will see at once that there is something there that holds your fingerprints, something that comes between you and the space outside.
In the same manner, the ground of the ordinary mind prevents us from breaking through to the skylike nature of our mind, even if we can still have glimpses of it. We have to break out of the ground of the ordinary mind altogether, to discover and let in the fresh air of rigpa.
—Tibetan Book of Living and Dying, chapter 16