ignorance

To cut identification with thought, we search for it and find it doesn't exist

Thought -- or rather, more specifically, taking thought seriously, 'identifying with it' -- is the root of all our dissatisfaction, unhappiness, and existential confusion. To pierce the identification, we repeatedly attempt to discern the background against which thoughts occur, and the end result is that identification is realized to be a fiction. No one was affected by it, no one pierced it. But paradoxically, great effort is required for this to happen.