Presumably William Blake had Plato’s allegory in mind when he observed, “If the doors of perception were cleansed, everything would appear to man as it is, Infinite. For man has closed himself up, till he sees all things through the chinks of his cavern.”
Blake, visionary that he was, saw more than most. Each of us however, sees but little; Blake, like the Buddha, appears to be saying that we are deceived by veils of illusion which originate within us. We can begin the process of broadening our perceptions, and raising our consciousness, by learning to recognise and tune out the chattering of the ego. Once we realise that the voice in our head, the relentless inner monologue, is the illusory voice of a false self, we can begin to disregard it, and so become tuned to other frequencies. Through prayer and meditation, we can raise a corner of the veil, or cleanse the doors of perception.