KAṬHA UPANISHAD · 1.2.5

अविद्यायामन्तरे वर्तमानाः
स्वयं धीराः पण्डितंमन्यमानाः ।
दन्द्रम्यमाणाः परियन्ति मूढा
अन्धेनैव नीयमाना यथान्धाः ॥ ५॥

avidyāyāmantare vartamānāḥ
svayaṃ dhīrāḥ paṇḍitaṃmanyamānāḥ ।
dandramyamāṇāḥ pariyanti mūḍhā
andhenaiva nīyamānā yathāndhāḥ ॥ 5॥

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 like blind men led by the blind.