One may think if there is, only one self why one is in pain another is in pleasure, everyone should have the same experience. The individual experience is a happening within the waking experience. The soul, which is the true self, witnesses the waking or dream as a whole. The individuality has no meaning because the waking itself is mere mirage on the standpoint of the soul as self.
The whole waking experience is a parallel dream. Whatever happening within the Waking experience is as unreal as dream. Until and unless the formless witness of the three states is traced mentally, the experience of duality will remain as reality.
Once seeker becomes aware of the fact that the formless substance and witness of the three states is soul/spirit and realizes the experience of duality is a mere mirage created out of the soul/self, Then the reality of the duality /mind gradually start subsiding.
That is the Seeker becomes fully aware of its true self and realizes the fact that, the formless substance of the three states itself is the witness of the three states. Therefore, the witness and the witnessed are one in essence.
Whatever experience experienced within the Waking or dream is only illusion. Only in the ignorance of the true self, the birth, life and death, the pain and pleasure are experienced as reality. When the waking itself is unreal what value they have in the realm of truth.
Since, the individual is ignorant of the formless substance and witness of the three states, which is the soul; he is bound to believe in the birth, life and death as reality. Once he realizes the self is not physical then he will realize whatever he knows, seen, believed accumulated and experienced as a person is part of the illusion because the here states are unreal on the standpoint of the soul, which is the true self.
The separation is felt within the Waking experience between one another and the world. There is no division is possible in the nondual true nature of the self/spirit. When this is realized, there is no second thing other then spirit/self.
Even in dream experience, there are millions of people and the dream world or cosmos, but they existed within the dream. The dream remains as reality until the Waking takes place. Same thing is applicable to Waking experience also. When the formless witness wakes up in its formless non-dual true nature, then the Waking experience is bound to be unreal.
The confusion and doubts exist until the whole thing is viewed on the standpoint of physical self/ego and holding Waking experience as reality.
Whatever objects, forms, and life is created and bifurcated by naming them with in these states of duality are created out of one and only material that is Spirit/Soul/Self. Realizing the fact that, there is no second thing other then the spirit/soul in this illusory experience of the duality will unfold the mystery of the true existence.