Anne Frank began documenting her thoughts in a diary because of the exceptional circumstances she faced while hiding from the Nazis during World War II. The diary served as a vital outlet for her emotions, aspirations, and fears, emphasizing the struggles of a young girl isolated from the outside world. Her reflections captured the human experience amidst the horrors of war and persecution, offering insight into her growing self-awareness and profound thoughts. Ultimately, her diary became a symbol of resilience and the struggle for identity under oppressive circumstances.