Katha Upanishad (associated with Katha Shakha of Krishna Yajurveda):
Prathama Adhyaya, Dvitiya Valli, Pancham Mantra (1.2.5)
अविद्यायामन्तरे वर्तमानाः स्वयं धीराः पण्डितंमन्यमानाः ।
दन्द्रम्यमाणाः परियन्ति मूढा अन्धेनैव नीयमाना यथान्धाः ॥ ५॥
1-II-5. Living in the midst of ignorance and deeming themselves intelligent and enlightened, the ignorant go round and round staggering in crooked paths, like the blind led by the blind.
2nd Valli starts with informing about difference between Shreya and Preya. Shreya means preferable, good or welfare for spiritual progress and approach towards the goal/Moksha whereas Preya means pleasurable which gives material/sensual pleasure. Wise man (who have true knowledge) prefer the preferable while others (due to the ignorance) prefer the pleasurable. That's why Gitapress Hindi translation writes Vidya and Avidya in the brackets to Shreya and Preya respectively.
So, Shreya and Preya equally approach man and who wisely examines and separates both and prefers the former while ignorant selects the later. This Vidya and Avidya are opposed to each other and lead to the different ways. The verse, which we're discussing presently shows the progress or marching of who selects the Preya over Shreya. Those who selects Preya, thinking that this is the right way, satisfies my desires and should be preferred over Shreya, go round and round staggering in crooked paths, like the blind led by the blind. Let's interpret 'blind led by blind'. Here those who have selected Preya are blind because they don't have true knowledge (still thinks that I'm intelligent and what I am selected is the best, Shreya) on what should be preferred, and Preya (Avidya) is also blind since it misleads as mentioned in Mundaka Upanishad (1.2.6) :
I-ii-6: Saying, 'Come, come', uttering pleasing words such as, 'This is your well-earned, virtuous path which leads to heaven', and offering him adoration, the scintillating oblations carry the sacrificer along the rays of the sun.
I-ii-7: Since these eighteen constituents of a sacrifice, on whom the inferior karma has been said to rest, are perishable because of their fragility, therefore those ignorant people who get elated with the idea 'This is (the cause of) bliss', undergo old age and death over again.
Coincidently, the next verse (1.2.8) is already cited by The Destroyer read the next verses which explains the predicament of ignorants.
So, Shreya is preferable, important, auspicious/welfare for the spiritual lord/master of chariot (see Katha 1.3.3) and leads to the supreme goal which is very subtle (1.3.10 and 11 or 1.2.8).
That's why Upanishads recommends us to approach the excellent preceptors:
प्राप्य वरान्निबोधत ।
क्षुरस्य धारा निशिता दुरत्यया
दुर्गं पथस्तत्कवयो वदन्ति ॥ १४॥
1-III-14. Arise, awake, and learn by approaching the exalted ones, for that path is sharp as a razor's edge, impassable, and hard to go by, say the wise.