I personally love that I have a pile of books I have bought but not yet read. Probably for the same reason that others have suggested – that it creates a sense of wonder and excitement there is so much more yet to learn:
These shelves of unexplored ideas propel us to continue reading, continue learning, and never be comfortable that we know enough. Jessica Stillman calls this realization intellectual humility.
People who lack this intellectual humility — those without a yearning to acquire new books or visit their local library — may enjoy a sense of pride at having conquered their personal collection, but such a library provides all the use of a wall-mounted trophy. It becomes an “ego-booting appendage” for decoration alone.