Sum up all the knowledge known, unknown and undetermined and that's a lot of stuff.
But to actually place that knowledge in categories is quite simple:
The things we know we know.
The things we know we don't know.
The things we don't know we don't know.
Think of what people are very sure about, but really don't understand at all.
It's almost that within a point in time which we have acquired the greatest amount of knowledge and have the easiest, fastest access to it, we really don't know much more than those who have gone before.