Perfect illumination gives rise to a perceived object; once the object is established, the illuminating nature is lost.

The Śūraṅgama Sūtra says: 圆明照生所，所立照性亡。The perfectly luminous bodhi radiance shines upon the dharma realm that He has brought forth. If someone takes this dharma realm as truly existent, as a real and indestructible dharma, as self or belonging to self, then it is like a single leaf covering the eye—one sees the false and not the true, failing to see the radiance of the wondrous luminous mind of ultimate reality, the self-nature. Thus birth and death flow on without cease.

When you write words on a blackboard with chalk, what are those words? They are all chalk dust. If you only recognize the words and not the chalk, the chalk dust is obscured. The chalk is a metaphor for the self-natured pure mind, the perfectly wondrous luminous true mind; the chalk dust is a metaphor for the self-nature's radiance; the words on the blackboard are a metaphor for worldly dharmas; and the blackboard is a metaphor for the worldly realm.