Historians look for several key factors when evaluating historical sources, and one of the most important is to assess if the source seems to have bias. Bias can affect the interpretation and reliability of the information presented, so recognizing it helps historians understand the context and perspective of the source.
While having a source that includes all the facts and presents multiple points of view is valuable, it is not always realistic, and historians often have to work with the sources available, critically analyzing their content for those biases and limitations.