Anne Frank decided to document her life in hiding as a means of self-expression and to cope with her situation. While in the secret annex, she felt isolated from the outside world and believed in the power of writing to articulate her thoughts and emotions. Her diary became a vital outlet for her fears, hopes, and reflections on humanity. Frank aspired to become a writer and recognized the importance of preserving her experiences, hoping her story would resonate and shed light on the horrors of war and persecution.