Diary Entries
A diary is usually a place for people to write their personal thoughts and feelings. It is generally not meant to be shared with others.
Historically, diaries have been an excellent source of information about historical figures. Once someone has passed away, a diary can provide details about the person's inner thoughts and perspectives.
Diaries suppose that the person writing the entries is a 'reliable witness' to the events; but it is important to remember that everyone is prone to bias.