MUṆḌAKA UPANISHAD · 1.2.8

अविद्यायामन्तरे वर्तमानाः
स्वयं धीराः पण्डितंमन्यमानाः ।
जङ्घन्यमानाः परियन्ति मूढा
अन्धेनैव नीयमाना यथान्धाः ॥ ८॥

avidyāyāmantare vartamānāḥ
svayaṃ dhīrāḥ paṇḍitaṃmanyamānāḥ ।
jaṅghanyamānāḥ pariyanti mūḍhā
andhenaiva nīyamānā yathāndhāḥ ॥ 8॥

They who dwell shut within the Ignorance and they hold themselves for learned men thinking “We, even we are the wise and the sages” — fools are they and they wander around beaten and stumbling like blind men led by the blind.