A closed system

Thought cannot examine itself in any ultimate sense – it is a closed system.  Thought can no more examine its own nature than a knife can cut itself, or an eye see itself.  The only way an eye can see itself is to avail itself of a mirror.  The nature of that mirror—vis à vis thought—is the natural reflective capacity of Mind, which is beyond thought.

p48, Shock Amazement: The four naljors and four ting-ngé’dzin from the Dzogchen series of the nature of Mind.   Khandro Déchen and Ngakpa Chögyam,  Aro Books Worldwide, 2018, ISBN 978-1-898185-45-1