सत्त्वपुरुषयोरत्यन्तासंकीर्णयोः प्रत्ययाविशेषाद् भोगः परार्थत्वात् स्वार्थसंयमात् पुरुषज्ञानम् ॥

sattvapuruṣayoratyantāsaṃkīrṇayoḥ pratyayāviśeṣād bhogaḥ parārthatvāt svārthasaṃyamāt puruṣajñānam

Enjoyment comes from the non-discrimination of the soul and Sattva which are totally different because the latter's actions are for another. Samyama on the self-centred one gives knowledge of the Purusha.

In plain words: We feel pleasure and pain because we mix up the true Self (Purusha, the pure soul) with the thinking mind (Sattva, the clearest part of nature). They are completely different, because the mind works for the Self, not for itself. By focusing deeply (Samyama) on the Self alone, the yogi comes to know the true Self.