And how could the Soul lend itself to any admixture? An essential is not mixed. Or of the intrusion of anything alien? If it did, it would be seeking the destruction of its own nature. Pain must be equally far from it. And Grief- how or for what could it grieve? Whatever possesses Existence is supremely free, dwelling, unchangeable, within its own peculiar nature. And can any increase bring joy, where nothing, not even anything good, can accrue? What such an Existent is, it is unchangeably.
Plotinus, The Six Enneads, The First Ennead