That’s the view that each era contains an important insight that is (unfortunately) mired in a confused set of errors. So, of course, it would be terrible to go back in total, but the nostalgia is latching onto what was good. And that good aspect is something we still need to pay attention to in the present. Hegel imagined an ideal history in which gradually all the good aspects of the past would be liberated from the unfortunate things that accompanied them.
