It is perfect example that a man need not be right to possess great wisdom. I have read some Dick, "UBIK" and "Eye in the Sky", but I never realized what a clever and introspective (and well educated!) man he was.

"Maybe each human being lives in a unique world, a private world, a world different from those inhabited and experienced by all other humans. And that led me wonder, If reality differs from person to person, can we speak of reality singular, or shouldn't we really be talking about plural realities? And if there are plural realities, are some more true (more real) than others?"

It reminds me of...

“Coming home from very lonely places, all of us go a little mad: whether from great personal success, or just an all-night drive, we are the sole survivors of a world no one else has ever seen.” – John Le Carre

Consciousness plays a role in the definition of the Universe, it is a fundamental part of it, not something that was added on at the last minute after billions of years of evolution. The pre-Socratics understood this! Physics tells us that the observation is both relative to the observer (Relativity ) as well as influenced by the observer (Quantum Physics). And Thermodynamics suggests information and entropy are inextricably linked. Physical phenomena cannot be understood without reference to purely perceptual, psychological (and social) concepts.

Reality is a meaningless concept unless there is someone there contemplating it, and even though,

"Reality is that which, when you stop believing in it, doesn't go away."

is absolutely a true statement, it is also an enormously misleading one.