The Chandogya Upanishad has a beautiful story about Indra, who lives with Prajapati for a total of 101 years to learn the truth about Brahman (Self).
For the first 32 years, Indra understands that Self asthe body.
He realizes that if body is hurt, Self will be hurt, body is blind, Self will be too and when body dies, Self too will die. He sees no value in such a knowledge.
For the next 32 years he understands that Self is that which moves about in joy in the dreaming state.
Soon, he realizes that it is true that the Self does not get hurt or blind or does not die in a dream state, yet, Self may appear to suffer and be conscious of pain and even weep. He sees no value in such a knowledge too.
For the third block of 32 years, he understands that Self is that which exists when the person is sleeping soundly, without any dreams, with a still mind.
Soon he realizes that the state of dreamless sleep is one that is not aware of oneself or any other. The state of dreamless sleep is very close to extinction. He sees no value in such a knowledge too!!!
So, he lives for another five years to learn the eternal truth about Self: the body is perishable, but within it dwells the imperishable Self. This body is subject to pleasure and pain; no one who identifies with the body can escape from pleasure or pain. But those who know they are not the body pass beyond pleasure and pain to live in abiding joy.
– Adapted in my words, from The Upanishads by EE, pg 144-151