According to the story of Ratanji, which philosophical teaching about happiness is presented in the book?

The story of Ratanji in Chapter 14 is used to illustrate a specific philosophical teaching about the nature of happiness. The text explains that it is a 'divine plan' that no one experiences unmixed happiness and that everyone has some nagging worry. Ratanji, who was outwardly 'swimming in an ocean of joy' with his immense wealth, was internally tormented by the 'crocodile of a difficult inner worry' over not having a son. Chapter 14 uses his situation to demonstrate that even the most prosperous individuals are not immune to sorrow, preventing them from becoming arrogant about their good fortune.