We have excellent evidence for the existence of our perceptions - we're immersed in the things, and we should not really doubt the reality of what is, after all, our only means of accessing data from the "outside world". The existence of the subject who is having these perceptions, however, may be thought, perhaps, to be a grammatical fiction, induced by the convenience of the subject-object relation in language, and drummed into our heads from childhood by the fact that we're always called by the same name. The 'inner viewer' or 'self' is much more in the nature of a hypothesis or a convenient manner of speech than a concrete reality, it might be thought. (From the thought of David Hume)
There is in every madman a misunderstood genius whose idea, shining in his head, frightened people, and for whom delirium was the only solution to the strangulation that life had prepared for him.
--Antonin Artaud