तदुपरागापेक्षित्वाच्चित्तस्य वस्तु ज्ञाताज्ञातम् ॥

taduparāgāpekṣitvāccittasya vastu jñātājñātam

Things are known or unknown to the mind, being dependent on the colouring which they give to the mind.

In plain words: We know a thing only when it affects our mind. If it leaves no mark on the mind, we do not know it.