We all keep stapling thin hardboard behind our bookcases, while this one panel swap is what really stops the shelves racking
That thin hardboard stapled to the back of your bookcase isn’t stopping it from wobbling—it’s just along for the ride. The real solution isn’t more staples or thicker board; it’s swapping that surface-pinned panel for one set into a rebate and screwed firmly in place, transforming a decorative afterthought into a structural brace.