यत्तु कृत्स्नवदेकस्मिन्कार्ये सक्तमहैतुकम्। अतत्त्वार्थवदल्पं च तत्तामसमुदाहृतम् ॥

yat tu kṛitsna-vad ekasmin kārye saktam ahaitukam atattvārtha-vad alpaṁ cha tat tāmasam udāhṛitam

While that which clingeth to each one thing as if it were the whole, without reason, without grasping the reality, narrow, that is declared to be dark.

In plain words: The darkest kind of knowledge grabs onto one small thing as if it were everything. It is narrow, has no good reason behind it, and misses the truth.