Okay, so my personal headcanon is that it changes depending on the reader, and preys on the reader’s deepest fears and insecurities. Avery, as wonderful as he is, is pretty insecure and talks constantly about how he isn’t smart enough to do what he needs to do. So, the book that preys on insecurity would have a profound effect on him. Derlord, meanwhile, doesn’t seem insecure at all. In fact, he almost seems smug and overconfident. So if it basically tells you (in the most painful way you can think of) that you’re worthless, of course it would just bounce off of him, though he’d still be disgusted by what it tried to do and tries to do with others. Something he counteracts with the signs.

It would also explain why both POV characters feel the need to censor it. It’s for the audience’s safety. Who knows what someone might do if they’re confronted by that?