We know a history so that we can learn from it. We learn our history because we understand the sacrifices that were made before, so that when we make sacrifices we understand we're doing it on behalf of future generations. There's a proverb that says, "We have not inherited this land from our forebears, we have borrowed it from our children.” In other words, we study the past so it can guide us into the future, and inspire us to do better.