A phrase can be used so frequently in a novel that quoting it becomes a coded signal you’re a fan of the book. The best example is ‘So it goes’ from SH5. It’s a motto, a tattoo, a stand alone Reddit post comment. For those who can’t place the quote it also serves as a cultural shibboleth.
But the only other ones I can think of are ’Es muss sein’ from TULoB and ‘Oh my valves!’ from CoD. (Why are all three words?!) But there must be others. I don’t mean famous one liners, I’m talking about multiple uses of a phrase. Can anyone mention another?
“It’s ineffable”
Also “inconceivable!” Though I haven’t read the book, so it might only be a movie line.
The Princess Bride and Good Omens make a good pair. I should read the former, I’ve only ever seen the movie.