If you don't know the mistakes of the present you're doomed to...?

The most appalling thing about reading history or at least about reading a good history is that you discover that people don't think the same way now that they used to, and back then they didn't think the same way as their ancestors. It makes you somewhat suspect that perhaps Reason isn't Supreme after all. I mean, the ancients had reason, the medievals had reason, and the enlightenment philosophers had reason, but reason never brought them to the same point.
The frightening thing is that we can't see the past the way those living in it saw it, and we never will. It makes you wonder if you're just a product of your age just as they were products of theirs. Then you say "Nah" and go back to watching the presidential debate.
Postmoderns would say that there's no way out. You're trapped. You can't think differently if you try, and you're not to be blamed, unless you are a white, male, capitalist oppressor. That is your fault.
But if you really know your history, it will do something for you. You may be able to see more than just the mistakes of the past. You may see the mistakes of the present.
Oh, and back to my other point about Reason. A modern examining the past ought to despair because he has been led to believe that it is pure Reason that makes him think what he thinks. He may, if he is honest, discover that it isn't.