My personal history is recorded in a variety of places. It's in the art projects on the wall of my old bedroom. It's in VHS tapes of childhood birthday parties and Christmas mornings. It's in the photo albums on my Mom's shelf, the emails archived in my Gmail account, the journals I've written in intermittently since the 6th grade. It's in the memories of my family and friends. If you gathered together all of these sources you could recreate a picture of some past experience of mine. But even though my history is recent and there are plenty of sources, the picture would be imperfect. It would be missing details. Some, forgotten. Others, intentionally omitted from the records because they weren't notable, or significant, or graceful.
This is how all history is written. Consequently, historians can only attempt to get as close as possible to what actually happened. What's more, the result is unintentionally skewed by the worldview and biases of the historian. A historian who has subtle, internal desires to find meaning in events and organization in chaos. He elaborates on what he understands and has no concept of things he doesn't understand. We cannot blame the historian. We are all historians.
If you look at the historical record, you'll see a general trend: The further we look back in time, the less we know. We can blame much of this on decay. We live in a dynamic world with forces of erosion, destructive organic processes, and tectonic activity. Nothing lasts forever.
When we piece together histories based on the records that haven't decayed, we get an even more partial view of history. Many times, we only see what the original recorders wanted to preserve. It's another layer of abstraction away from the truth. First, the truth is filtered by what we chose not to record. Then it is filtered by what we chose not to preserve.
Even if some information survives both filters, we cannot properly understand it without contextual information that didn't survive the filters. That's why it's so hard to answer questions like how atrocities like the Crusades or the Holocaust could have happened. It's hard enough for us to put ourselves in somebody else's shoes. To truly do it accurately for somebody who lived 400 years ago… that's nearly impossible.
So what DO we actually know?
We know a lot of information. Names, dates, sequences of major events (or events that seemed major to the people recording them). We know about battles, heroes, cities, religions, discoveries and philosophies. We know about many of these things in great detail. Sometimes by reading the interactions of people in ancient books or plays, we learn a little bit about how people lived. What they thought was important. Where they spent time. Their desires, fears, and sorrows.
But those samples are few and far between. Certainly, they don't represent all the cultures and classes of citizens through the various periods of time. And when you think about how different your life is to the novels you read or the sitcoms on TV, it's easy to see that those ancient works won't paint a complete picture.
The biggest issue is that we don't know what we don't know. Like I said before, the world is a lot messier than we tend to portray in history books, and only a tiny fraction of the total sum of historical information survives. When we look at history with a 21st century worldview, we easily miss details about public opinion, social pressures, and other nuanced topics. We instantly assume that we are smarter, more informed, more disciplined, more principled, and more enlightened then they were. That perspective radiates self-serving bias, and it is incorrect.
Why does this matter?
In most cases, it doesn't. History doesn't help me decide how much bus fare to buy or which books to check out from the library. It has very little impact on my decision making process. However, historical misunderstandings can cause bitterness in all sorts of situations, from long held grudges and family feuds to racial and religious intolerance. Those things are so bogus. It doesn't matter if it's 2, 20 or 2000 years old, if you have beef with something that happened a long time ago, then you have to realize that you know almost nothing about what actually happened. Your beef is with an imaginary reconstruction of the truth that exists only in your mind. Life is too short to hold fiercely onto such biases when we live in a world that desperately needs more positive influences. Everybody deserves the benefit of the doubt.
Including those who came before us.