why did anne decided to write the diary? What role did this diary play in her life.

Being a thirteen year old girl, Anne wrote her diary for the same reasons any adolescent girl might write a diary. She wanted to chronicle her feelings and make sense of the world around her. Of course Anne was living in a pressure cooker. Hiding from Nazis with so many people in a small annex was not easy. Ann used her diary as a therapy to cope with not only teenaged angst but to keep perspective and her sanity in such a close environment. The original diary wasn't to just "Kitty" but to many pseudonyms. The diary became a sounding board for Anne and, eventually, a passionate piece of historic evidence for the world.