The mind is something that has intrigued mankind throughout the ages. What is it? How does it work? These are questions that have perennially been asked. Like a mirror, the mind is able to bear the image of all appearances and make them known, yet when you search for this mirror, it cannot be found – it is as if transparent. A clear, lucid awareness of objects, yet impossible to pinpoint: this is the mind.
Sometimes, however, the mind's mirror is fogged and everything is hazy. At other times it is clear and empty with nothing appearing, while at others it is churning with thoughts as if in a race. But whether it is a sight, a sound, a thought or whatever, there is nevertheless a quality of brilliant, yet unfindable, awareness pervading it that remains the same. When you are aware of it, you are not fooled into becoming disturbed over what appears in the mirror of your mind. You know its abiding nature and no matter what occurs, you are "calm and clear." But if you are unaware of what is actually happening with your mind and thoughts, the images in the transparent mirror become concrete and heavy, causing you anxiety, desires, fears and delusions. Insecure, not knowing what you are experiencing, you incur great suffering and uneasiness. Everyone around you is similarly confused and bewildered, and if you cannot pull yourself out of this state, how can you possibly help them out as well? The critical point, then, is to know your own mind.
from the Preface to The Mahamudra — Eliminating the Darkness of Ignorance by Wang Ch'ug Dorje, the Ninth Karmapa