Bhagavad Gita 2.16नासतो विद्यते भावो नाभावो विद्यते सतः।उभयोरपि दृष्टोऽन्तस्त्वनयोस्तत्त्वदर्शिभिः ॥

-- The changeless, homogeneous Atman or the Self always exists. It is the only solid Reality. This phenomenal world of names and forms is ever changing. Hence it is unreal. The sage or the Jivanmukta is fully aware that the Self always exists and that this world is like a mirage. Through his Jnanachakshus or the eye of intuition, he directly cognises the Self. This world vanishes for him like the snake in the rope, after it has been seen that only the rope exists. He rejects the names and forms and takes the underlying Essence in all the names and forms, viz., AstiBhatiPriya or Satchidananda or ExistenceKnowledgeBliss Absolute. Hence he is a Tattvadarshi or a knower of the Truth or the Essence.What is changing must be unreal. What is constant or permanent must be real.