In the state of deep sleep, when ego disappears and the body and the world also disappear, which indicates the ego, body and world appear together and disappear together. The dream is parallel waking experience and waking is parallel dream. The witness of the three states is apart and eternal. Ignorance of this formless witness or knower of the three states makes one to judge the three states on the waking entity.
The waking entity is not the self. The self is the one which is aware of the three states. The waking entity is noting to do with the self, because the waking experience itself is falsehood on the standpoint of the formless witness. Judging the truth on the base of the waking entity will lead one to imagination and intellectuality. Intellectuality is based on the false self or waking entity or ego and yield only half truth.
There is a need to proper and perfect understanding of the Self. The self has to be mentally grasped. For sharp mind it takes a very little time to grasp, for others it takes a long time to assimilate and realize it. When one becomes aware of the fact that, the witness of the dream witnessed the whole dream without the physical eyes, they become aware of the existence of the formless witness, which witnesses the three states without the physical eyes.
Nature of the Atman (soul) is formless and non-dual. It is associated with the three states as their formless substance and witness. When the ego is identified as self then there is ignorance.