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?

Literary Analysis
The Hitchhiker’s Guide to the Galaxy

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.