Puruṣa or Self is described in Upaniṣads as unseen, unusable, unperceivable and unmanifest. Since Puruṣa is attributeless it can only be understood through negation (it is not this, not that, etc). When one attains a state, it necessarily means one “mutates” from one state to another. Therefore, if Puruṣa is unseen, unmanifest and unperceivable, what does Self realisation or attainment really mean? That does not seem to make sense.
Yoga Sūtras offer a clarification.
Sūtra 3.55 | sattva puruṣayoḥ śuddhi sāmye kaivalyam
Sūtra 3.55 is a spectacular statement. It essentially says that by cleansing the mind off action (Rajas) and inertia (Tamas) one attains kaivalyam. A mind with out Rajas and Tamas is said to be full of Sattva and that is as close as one gets to Puruṣa.