At a certain scale, the study of history can be a very difficult thing to navigate. With the intensity of our collective instruments of research, and our access to the vast amounts of information and inquiry now possible, we have a very long timeframe to account for now, which is suffused with an incredible richness of knowledge wherever you look. And with each new day, we make more history.
If you choose any given historical period, you find that as you go deeper into that period, there is more and more to know, and more going on than you previously imagined, and that it was all simplification upon simplification in the history books, and even in our best efforts, and our cutting edge research.
You can see how a given scholar can dedicate their entire life to a certain smaller period of time, or even region or limited subject. Poring through the historical record, you see name after name, relation after relation, event after event, and almost immediately in any given procession of events, the mind begins to melt. It takes a gifted person to organize all of that into a compelling narrative that works, so it becomes very important to learn from gifted individual thinkers covering a variety of topics throughout history to even begin to make sense of it all.