"Her Second Thoughts added: I wonder how many have got in already and we don’t know? And I am in Fairyland, where dreams can hurt. Somewhere all stories are real, all songs are true. I thought that was a strange thing for the kelda to say.… Tiffany’s Second Thoughts said: Hang on, was that a First Thought? And Tiffany thought: No, that was a Third Thought. I’m thinking about how I think about what I’m thinking. At least, I think so. Her Second Thoughts said: Let’s all calm down, please, because this is quite a small head."
January 1, 1970
https://en.wikiquote.org/wiki/Discworld