Judging from the issues he treats in his mature writing, he felt that his intellect might overbalance the development of his other gifts to the detriment of expressing his total being. Perhaps Blake's early unfinished prose satire, An Island in the Moon, with its frivolous, clever approach, represents a succumbing to the temptation to allow the intellect to have free rein to dominate and go in directions that his identity would not choose, and which would quash the development of imagination and desire.
In his student days, Blake scholar Joseph Viscomi adapted the satire for a production which was presented at Cornell University. Read the manuscript of Island in the Moon in Blake's complete works or learn more about it on Wikisource.
Blake did not pursue the avenue of writing, thinking or entertainment displayed in An Island in the Moon. His fans believe that he went on to other and better things.
Morning Chasing Away the Phantoms
from Milton's Paradise Regained
Sensation, reason, and emotion are all subject to being overvalued, distorted and corrupted. Blake's desire to 'cleanse the doors of perception' represented the efforts he put into removing the impediments from expressing the Identity. Through attempting continually to annihilate the Selfhood, Blake tried to avoid allowing the fallen sensation and intellect to mar or replace the Eternal intellect and sensation which he trusted and valued.
Vision of the Last Judgment, (E 554)
"The Last Judgment when all those are Cast away who trouble
Religion with Questions concerning Good & Evil or Eating of the
Tree of those Knowledges or Reasonings which hinder the Vision of
God turning all into a Consuming fire
Science & all Intellectual Gifts all the Gifts of the Holy Ghost
are [despisd] lookd upon as of no use & only Contention
remains to Man then the Last Judgment begins & its Vision is seen
by the [Imaginative Eye] of Every one according to the
situation he holds"