Primary sources are usually considered to be the most desirable by historians when reconstructing the past. However, since primary sources are by definition personal accounts of people living inside history, they are subject to the same distortions of bias and time-bound perspective as any contemporary eyewitness account would be. What are some of the circumstances that might make a primary source "unreliable" or at least unsuitable to stand alone when examining an historical event, i. e., the personal journal of a slave-owning Confederate general during the Civil War, an anti-colonial British commander during the American Revolution, etc...