There's a short entry in the first pages of a book, the title and author of which I can't remember but whose concept is awesome enough for me to want to find it again. The short version is, "This story is a work of fiction. It did not really happen. However, for those within the story itself, the fiction is real. In this way, perhaps all works of fiction are also real. Thus, all worlds exist, even if the only evidence of their existence in ours is fiction."
The nature of the text itself makes it an impossible search. 9 billion articles on "works of fiction", "the existence of worlds", "the autonomous reality of existence does not really exist" are in the way. I've actually been trying to help you search for this since you posted it because I know how itchy this particular kind of itch can be. You have my sympathies. And I apologize for the let-down this post must be because I'm sure you were thinking, "Yes! Someone has the answer!!" Is there any one piece that you feel you remember more accurately than the larger whole? Don't give up hope. I had a book that I was trying to find for the longest time and all I had to go off of was my memory that the handedness of molecules was a strong plot device in the story, there were crab-lookin' aliens, and someone ate a "banana" that was mentioned to have a "pit" because it turned out it wasn't a banana at all and the person who ate it did so as the victim of a prank because whatever fruit it really was was the wrong handedness of molecules for human digestion. Dreams of Dawn by Marti Steussy.
The ubiquitous nature of the message is rather why I'm having the problem =( I know it's from a relatively well-known author and every author has their devoted fanbase. It's the kind of thing devoted fan would remember - just hoped one of them would happen to pass by here
