The hardest part of studying history is knowing how to factor out the ideas that were inconceivable to the actors of history at that time — and grasping the impact of how an absence of these concepts might change how events might seem.

It is not mere absence of fact, it is absence of an ability to even see a fact if it is standing before you staring into your eyes. If you are having difficulties knowing what I mean by this — and many do! — others who will come later will have difficulty grasping how it was for you to look through this concept without seeing it.