Historians face unique challenges. We sometimes have very little evidence about the past. When we do have evidence, which includes written records, artifacts, human remains, and ruins, the written sources are sometimes biased and sometimes include people's opinions.
Also, we must use sources which are credible. Anyone can post information on a website. That does not mean what they present is factual.
Finally, what we think we know today about the past could change tomorrow with a new discovery.Â