I've thought of denial as a way to not have to face something painful until one is ready to face it. I know I lived in my own denial hell for a while.
I've been through mental illness with my loved ones, so I understand how brain disorders work. The person experiencing them is always the last to know. I remember one person in Al-Anon talking about her AH watching the rehab shows on TV and being very judgmental about the people portrayed, and then congratulating her for going to AL-Anon and "fixing herself".