Why does Winston decide to write a diary despite the consequences ?

Winston's soul is full of discord. At times he feels dead inside and at times he is full of rage. He has no outlet for any of his feelings. He always must be vigilant to look "normal" because the thought police may be watching. Winston needs the diary as an outlet to remember he is alive and to experience some type of release from the tumult inside of him. I think it also provides the illusion of hope for Winston that the future may be different than the party controlled present.