What is the best example of a primary source document useful in the study of history?

One of the best examples of a primary source document useful in the study of history is the Diary of Anne Frank. This firsthand account provides insight into the experiences of a Jewish family hiding during the Holocaust, reflecting the emotional and psychological realities of that time. It offers valuable perspectives on human resilience, persecution, and the impact of war, making it an essential resource for understanding this historical period. Additionally, primary sources like this help historians connect personal narratives to broader historical events.