The previous post helps me see that the separatio happens in two ways: unconsciously and consciously.
Undifferentiated and nonfunctional unity
First, there is an unconscious and undifferentiated unity of the individual and the world as a whole. But since it is undifferentiated, it is also nonfunctional. We all start out on our human journey as helpless and dependent on others.
This unity does not go away, it is the ground of existence (and the prima materia), but it may appear as split later on in the process. The dependence on others does not go away either, for that matter, even if that too may appear differently later on.
Unconscious separatio: a sense of I and Other
Then, there is a mostly unconscious separatio. A sense of a separate I, of I and Other where I is this human self (or an aspect of it) and Other is anything else: anything outside of this human self and anything from inside this human self that doesn't fit with what the personality wants (for instance pain, anger, sadness, etc.) We inadvertently split the world into I and Other, partly because those around us do it.
Conscious separatio: differentiation and discernment
The next separatio is more conscious. It is a process of discernment and differentiation, of exploring the different aspects of the whole, how each one functions, and how they relate to each other. This happens in the ordinary process of developing and living our lives, and with more heat and specificity if we consciously engage in a process of individuation or awakening.
The unconscious separatio sets the stage for the conscious separatio
The unconscious separatio sets the stage for, and aids, the second separatio. It creates a sense of a split that makes it easier to consciously differentiate and discern. There is a gap allowing for some distance and perspective. The inevitable stress from the first separation, the sense of I and Other, also provides the motivation (the nigredo) for the second separatio to take place.
The conscious separatio allows the unconscious separatio to fall away
And the conscious separatio, exploring the polarities and how the sense of I and Other comes about, allows the first separatio to eventually fall away.
The first gives birth to the second, allowing the first to fall away. It is a stepping stone which is left behind at some point. (At the same time, the basic ego-structures developed during the first separatio, and refined and reorganized in the second, remains. They are the ones which allows this human self to function in the world, to orient, navigate, be effective.)