how is history not reliable, even when there are documents to prove it?

I've wondered about this topic many times. I learn history, I remember dates and people. Yet still there's a side of me that wonders “what will I ever do with this subject?". If you look back on different events in history, something can help you change your perspective. I think this is a class that changes your character. When young African Americans today learn about all the different heroes that granted their freedom today, they learn to respect. When the youth today faces conflicts with the older generation they can look back through history and see when their parents too faced those conflicts and maybe can learn to compromise. The tragedies that the past has faced will reflect our future. The things that have already happened we learn today can change our choices and try to make a better one that won't result in violence or other bad outcomes. History indeed should be taken seriously as a core subject. You have to live in the future, but where would that be if it wasn't for the past.