Kristy Logan writes about why she loves unread books, in short, because they can never disappoint:

An unread book is all possible stories. It contains all possible characters, styles, genres, turns of phrase, metaphors, speech patterns, and profound life-changing revelations. An unread book exists only in the primordial soup of your imagination, and there it can evolve into any story you like. An unread book – any unread book – could change your life ...

... As much as I enjoy the books, I often find that the book I have read is somehow not as exciting as the book I had imagined reading. No book is ever quite as good as it potentially could have been.

But what about the book that surprises us, the one that we had to read for an assignment or a book club that blows us away?  In that case, the unread book could feel like a burden, and the real payoff is in its finished state.

Logan later suggests that a love for books makes us conjure the best possible outcome for each volume, thus the inevitable letdown.  "I suggest that the literary universe you just created might be more exciting and enlightening than the one contained within those covers," she says.  This is true, but unread books on my shelves mostly make me feel guilty, either for never getting around to reading them, or spending the money in the first place.