For example, on my top reading shelf is part of my chess collection. Besides the literally voluminous row of John Watson's Mastering the Chess Openings series, I've placed a few other books from the same publisher and a Practical Endgame Play: Mastering the Basics by Efstratios Grivas. Next to Grivas, of course, is Glenn Flear's Practical Endgame Play: Beyond the Basics.
And beyond the beyond? I note that this is where my collection of guides to philosophy and my little collection of theological philosophy by Peter Kreeft. Indeed, my Handbook of Christian Apologetics by Kreeft and Tacelli sits right next to Flear's book.
It's interesting to see how those books got there. You would guess at several reasons. But you would possibly be wrong (indeed, since there are fewer real reasons than guesses, some of you would certainly be wrong).
Meanwhile, I marvel at my subconscious ingenuity.