You can not "pin down" the self, because it is not a thing.

The ego is a thing, it is a construct. Easy to see. But the self cannot be defined. No thing has no attributes or features by which to define it.

What can be defined and understood, is the projections of the self which is duality.

The self can only ever be experienced. This is why many mystics have used the "via negativa" to reach it. What is God not? "He" is not any of his projections.

What is attempted by using the via negativa, is to reach the "ground of being". And the negative path does that. Through that path, it is discovered that God is no thing.

When having used the via negativa, one must turn around and ask the opposite question, "via positiva". Through that path, it is discovered that God is everything.

This dual yet non-dual insight is the unity of opposites - Alpha and Omega, the beginning and the end. It’s not a contradiction but a paradox, pointing to the ultimate truth that transcends and includes all polarities.

Nothing lasts forever. Something does not.