The one lesson is this: you have to consider ALL effects of economic intervention. The author claims that too many people intervene in the economy by only considering the effect on one group of people, not acknowledging that their change has also affected another group.
The author is from the Austrian school, and seems to think that the government should NEVER intervene in the economy. He seems to argue that no intervention can ever increase wealth, because it simply takes from one group and gives to another, so no one gets any wealthier.
Clearly, he’s a politically conservative dream. I didn’t agree with all of it, but it’s well-written and well-argued. But only four stars because it just gets ridiculously repetitive.