This sentence comes from Hegel's Philosophy of History. The only lesson that mankind has learned from history is that it has not learned any lessons from history.

The reference before and after the "lesson" is different. The latter refers to the experiences and lessons that human beings have gained from various historical events, while the former refers to the conclusion that human beings have summed up these experiences and lessons: human beings are always repeating the same mistakes.

So what Hegel really wants to say is that, just as people can't cross the same river twice, the situation that a country encounters every time is brand-new and unique, so we can't stick to dogma and copy historical experience.

Extended data

Hegel's view of state inherits and develops the tradition of German classical philosophy since Kant and Fichte. He used philosophical speculation to reveal the essence of the country, and opposed the social contract theory of 17 and 18 century to explain the essence of the country from its external characteristics, arguing that the country is not an arbitrary product of the contract.

His concept of state refers not to the existing state system, but to the spiritual concept of state. He believes that the realistic state is only the expression of the concept of state. The essence of a country is that it is the reality of ethical concepts and an absolutely self-sufficient rational thing.