A few weeks ago I was looking for a book on my language shelves. I noticed a book called A Study of Writing by I. J. Gelb. Separated from it by two or three books was another book (of a slightly different age and color, but identical size) called A Study of Writing by I. J. Gelb.
I had never before noticed that there were two copies of that book, not even when I arranged the language book shelves roughly by topic.
My immediate response was to remove the older copy. And to then insert it next to its duplicate on the shelf.