Jose Luis Borges wrote a story about the Library of all Possible Books, and this concept has fascinated many authors. When young, I read an essay about this library that intended to help me better understand large numbers and infinities. Imagine a library that contains every possible book. (Don't think about the niceties of placing a limit on the size of these books, to make this an exercise in finite numbers; it'll make your head spin.) You can imagine that somewhere in this library there is an index to all the books in it. But if you think you've found that book - maybe you've actually found a book that is an index to all the books in the library except for one tiny mistake, or ten big mistakes; or maybe it just LOOKS like an index to this library, but every book it names doesn't exist. (Is that possible?)
When I was young, the "library of all possible books" was an interesting, if impractical meme. But today: we have the internet! As the internet's collection of web pages grows, it resembles, more and more, and with all its warts, the Library of all Possible Books.