The fact that you need an electric drill was a difficulty, also the instructions are only in English, and I struggled to understand what a stud is. To help someone else, they are wooden beams that are on the walls on the outside, and it tells you to secure them there, but in traditional Greek apartment buildings we don't have them, so they don't concern us. Oh, also, in order for the shelf to be invisible, the bottom book needs to have a hardcover, that's how invisibility works, you secure it to some hidden pegs. Anyway, if you manage to do it, it looks very nice.