People with absurd numbers of books (like tens of thousands) will justify them by saying they fully intend to read them all one day, or they're of sentimental value, or they can't bear to part with old favourites, or they're related to a particular interest (like hundreds of bird books).
Jenny and I have always kept our book stock to a modest level - about a thousand books at the last count - by aiming to discard as many books as we buy. This routine has served us well so far. Luckily there's a charity second-hand bookshop just down the road. so our abandoned books will find new readers. Of course we may simply be encouraging book hoarders to buy dozens of cheap second-hand books....
There's a temptation to acquire as many books as your home can accommodate. The first flats Jenny and I lived in were too small for large numbers of books, so we were more likely to "read and discard", but as we moved to bigger flats the need for a rapid recycling of books declined and they tended to linger.
We keep a lot of books on the basis that we're sure to re-read them some day, only to find that many of them never get re-read and just gather dust. Sooner or later our tastes change and that wonderful old book from ten years ago suddenly seems clunky and rambling and ready to be thrown out.
At least I don't buy books I know very well I'll never read, like Ulysses or War and Peace or In Search of Lost Time. That's a few less to worry about.
