The Manifest and the Unmanifest
All that is ever known are the particular manifestations of reality within an individual's experience. The unmanifest, the underlying reality, remains unknowable.
To illustrate the relationship between these two aspects of reality Indian teachings often use the analogy of waves on an ocean. The ocean is the unmanifest, Absolute, level of reality. Its essential nature never changes; it is always simply water. What changes are the waves produced on the ocean's surface as it is stirred by the wind.
Shining on the ocean's surface is the sun -- the light of pure consciousness. When the ocean is still, it is a perfect mirror; and perfect mirrors are, in a sense, invisible. You never see the mirror itself; just the image that is reflected back. For most of us, however, the mind is never still. It is always being stirred in one way or another by activity in the brain. Sometimes it may be activity stemming from our sensory perception, at other times, as in sleep, the activity may be coming from past memories or other sources.
The various manifestations of the ocean -- the waves on its surface -- are only visible by virtue of the light reflected back. Each little wavelet reflects the light in many different direction, producing its own little transformation of the sky above. We don't se the sun anymore; instead these many little reflections create a pattern that we see as the waves on the surface. So too, all the little disturbances of our own consciousness together create an image of reality within our mind. We do not experience consciousness itself; only the myriad of manifestations that it takes on.