The psychotic does not merely think he sees four blue bivalves with floppy wings wandering up the wall; he does see them. An hallucination is not, strictly speaking, manufactured in the brain; it is received by the brain, like any 'real' sense datum, and the patient act in response to this to-him-very-real perception of reality in as logical a way as we do to our sense data. In any way to suppose he only 'thinks he sees it' is to misunderstand totally the experience of psychosis.
Philip K. DickHow'd you like to gaze at a beer can throughout eternity? It might not be so bad. There'd be nothing to fear.
Philip K. DickWhat scared me the most was when my father would put on the gasmask. His face would disappear... This was not a human being at all.
Philip K. DickI want to write about people I love, and put them into a fictional world spun out of my own mind, not the world we actually have, because the world we actually have does not meet my standards. Okay, so I should revise my standards; I'm out of step. I should yield to reality. I have never yielded to reality. That's what SF is all about. If you wish to yield to reality, go read Philip Roth; read the New York literary establishment mainstream bestselling writers
Philip K. DickWhy does a man cry? he wondered. Not like a woman; not for that. Not for sentiment. A man cries over the loss of something, something alive. A man can cry over a sick animal that he knows won't make it. The death of a child: a man can cry for that. But not because things are sad. A man, he thought, cries not for the future or the past but for the present.
Philip K. Dick