What is one of the universal messages the novel conveys? In other words, what is the central idea, which is unified around the characters and the plot?

Book: The Hitchhiker’s Guide to the Galaxy

Topic: What is one of the universal messages the novel conveys? In other words, what is the central idea, which is unified around the characters and the plot? Theme is not a topic nor Hallmark card; it should be expressed as a sentence about human nature.