Yōga Sūtra 2.17

द्रष्टृदृश्ययोः संयोगो हेयहेतुः।

draṣṭr̥dr̥śyayōḥ saṁyōgō hēyahētuḥ।

[द्रष्टुः दृश्ययोः संयोगो हेय हेतुः।
draṣṭuḥ = the observer; dr̥śyayōḥ = with the observed; saṁyōgō = the union of; hēya = must be destroyed; hētuḥ = is the cause;]

The union of observer with the observed is the cause and must be destroyed.

Here an investigation begins into the cause of obstacles. At first level, the union of the observer and observed is the cause and must be eliminated.