Blake often tells the same story from the viewpoint of various characters. In the Book of Urizen, we see the Fall from Urizen's perspective. The breaking apart of the unity of Eternity results in Urizen finding himself in a void, formless yet dividing. There is, as yet, no outer reality, but the inner activity of Urizen begins to construct a mental world of uniformity, stability, laws, secrets and sins.
Is this a tale of the formation of the psyche from the point of view of the Superego? Comparing itself to the Id, the Superego would see itself as reason, self-control, necessary restraint, the means of functioning in the world. But the consequences of emerging from the undifferentiated whole, would not be apparent to the emerging Superego.
Urizen, the setter of limits, is without limits himself. So Los the vehicular form of the Zoa Urthona, is assigned by the Eternals 'to confine the obscure separation alone.' (BU5:40;E73) Los, 'Cursing his lot,' undertakes the task of creating a world and a form in which Urizen can function.
In Blake's scheme error is a state which can be destroyed once it is recognized and limited. Urizen's system is allowed to develop until it can be recognized as error.
Book of Urizen, Plate 16 (BU15.5; E78 )
"The Abyss of Los stretch'd immense:
And now seen, now obscur'd, to the eyes
Of Eternals, the visions remote
Of the dark seperation appear'd.
As glasses discover Worlds
In the endless Abyss of space,
So the expanding eyes of Immortals
Beheld the dark visions of Los,
And the globe of life blood trembling"
The process of differentiation continued with the division of Enitharmon (space), Orc (energy or change), Thiriel (air), Utha (water), Grodna (earth) and Fuzon (fire).
Urizen is not pleased with the emerging world: 'Urizen sicken'd to see His eternal creations appear.' Apparently it doesn't measure up to the world he left in Eternity.
He realizes: 'That no flesh nor spirit could keep His Iron laws one moment.'
Urizen wanders about the world spinning the web of religion, carving the laws of God and unable any longer to see into the closed tents of the Eternals. Urizen, the Superego, has created a dilemma; he can say 'Thou shalt not,' but he can't say 'Thou shalt.' (“Without a vision the people perish.” Proverbs 29:18.) Urizen is at an impasse from which he cannot extricate himself. The divided self, without the Spirit or Imagination lacks the ability to live the life of joy, peace, forgiveness and brotherhood.
The rest of Blake's myth deals with healing the division and restoring the psyche to Eternity (and of course, telling of the tale from other points of view.)