I find placing books into bookcases horribly frustrating and difficult when the intent is to keep the book readable.
Basically when you place a book in a bookcase shelf, if the book touches the shelf in anyway you can no longer interact with the book to read it.
Very tedious and careful placement allows it to work if you leave the spine of the book hanging off the shelf some ways, but if you screw up the placement of ONE book you can no longer select it to move it, and you have to use the retrieve function, which is only viable if you remember exactly which book it was.
Or, remove the shelf, move the books and start all over again