Sri Aurobindo translates Katha Upanishad, First Cycle: Second Chapter, Verses 5-6: “They who dwell in the ignorance, within it, wise in their own wit and deeming themselves very learned, men bewildered are they who wander about round and round circling (1 doubtful reading) like blind men led by the blind. The childish wit bewildered and drunken with the illusion of riches cannot open its eyes to see the passage to heaven: for he thinks this world is and there is no other, comes again and again into Death’s thraldom.”
The Upanishads repeatedly make a distinction between what they term the “Ignorance” and what they term the “Knowledge”. The Ignorance is the limited view fixated on the life of the world. It focuses on learning how to manipulate the physical, vital and mental forms and forces and thereby attain success in the world based on a variety of criteria, including physical survival, satisfaction of needs and desires, fulfillment of ambition and achievement of fame and persistence in the world. All of this is termed the “Ignorance” because it ignores the deeper significance and truth of existence. The result of this fixation on the outer world is subjection to sickness, old age, pain and suffering and death. Every enjoyment obtained eventually leads to suffering.
The Buddha treated this relationship between focus on the outer world and suffering and death as a basis for his teaching. The Katha Upanishad identifies this relationship very clearly.
The “Knowledge” recognizes that this world is part of a larger divine manifestation; that the knowledge of Brahman is the key to transcending the limitations of life and death and the travail of suffering. This does not imply necessarily that the events and experiences of the outer life will be any different, as the laws of life and death obtain here, but the individual who has recognized the truth of the Spirit will respond from a different standpoint that can accept both joy and suffering, pain and pleasure, success and failure as elements of the manifestation that do not attach themselves to the seeker. The key difference is the removal of the ego-standpoint as the basis of the judgment and response, as the individual shifts to the divine standpoint.
Sri Aurobindo, The Upanishads, Katha Upanishad, pp. 213-241, and Kapali Sastry, Lights on the Upanishads, pp. 104-129