Hazlitt's "one lesson" is simple, and told in Chapter 1. The rest of the chapters are all stories in which the lesson plays a prominent role. In short, Hazlitt doesn't merely tell us the lesson, he actually shows us the lesson --in rich variations.
With stories on tariffs, minimum wage, rent controls, taxes. unions, wages, profits, savings, credit, unemployment, and so much more, Hazlitt takes some of the most difficult economic concepts and makes these easily accessible to the lay person who has no economic training, background, or even inclination.