“In the universe, there are things that are known, and things that are unknown, and in between, there are doors.” 

- W. Blake (or maybe Jim Morrison, or maybe Aldous Huxley)

Blake believed that human beings were severely bound in their experience of the true universe by the limitations inherent in their human senses. Due to his own experiences with visions and prophesies he believed he possessed a kind of super-human perceptive capability that allowed him to see deep truths. His "doors of perception" were thrown wide while we were perceiving the world through "narrow chinks" in our own personal "caverns."

Blake's phrase "doors of perception" would, much later, be embraced by Aldous Huxley and other users of psychedelic drugs who claimed they were throwing wide their own doors.

“If the doors of perception were cleansed every thing would appear to man as it is, Infinite.

- W. Blake (definitely)