kena upaniṣad - dvitīyaḥ khaṇḍaḥ

If you think that you know Brahman well, then you know but little; you know only the aspect of Brahman that resides in beings and in the gods. Therefore, you must still reflect upon what is yet to be known of the Absolute.

I do not think that I know Brahman well, nor do I think that I do not know Him. He among us who understands the meaning of this—that Brahman is both known and unknown—he truly understands.

He who thinks that Brahman is not understood, understands Him; he who thinks that Brahman is understood, does not know Him. Brahman is not understood by those who claim to know Him, but is understood by those who realize they do not know Him.

Brahman is known when He is realized in every state of consciousness, for thus one attains life eternal. Through the Self one gains strength, and through Knowledge one attains immortality.

If one realizes Brahman here in this life, then there is truth; if one does not realize Him here, then there is great loss. The wise, seeing the Self in all beings, depart from this world and become immortal.