C.S. Lewis:

It is a good rule, after reading a new book, never to allow yourself another new one till you have read an old one in between. If that is too much for you, you should at least read one old one to every three new ones… People were no cleverer then than they are now; they made as many mistakes as we. But not the same mistakes. They will not flatter us in the errors we are already committing; and their own errors, being now open and palpable, will not endanger us.

This quote amused me because it certainly feels like we are making the same mistakes. I suspect our lack of reading about the past (new or old books) leads to Dunning-Kreuger style hubris where we commit the same mistakes.