The number of the beast.

Heinlein buff David Potter explained on alt.fan.heinlein, in a posting reprinted on the Heinlein Society, that the entire book is actually "one of the greatest textbooks on narrative fiction ever produced, with a truly magnificent set of examples of HOW NOT TO DO IT right there in the foreground, and constant explanations of how to do it right, with literary references to people and books that DID do it right, in the background." He noted that "every single time there's a boring lecture or tedious character interaction going on in the foreground, there's an example of how to do it RIGHT in the background."