Why do some peoples brain stop working?

When my aunt became legally insane, all i could think of was of the great times i had with my godmother. I could’nt stop thinking of all those times i noticed her twithcing her fingers, zoning out, and talking out of content. No matter what we always loved her, and thought she was great! My aunt had been with my brothers and I since i was born. Always taking care of us, picking us up from school, cooking dinner and lunches, watching old nick at night shows with her, and telling stories of when she was young in the late 50’s. My father had told me that she had always had a little bit of a problem. She had never wed, no boyfriend, no children, and was always under the care of my grandmother. I can remember she will always be smoking a cigarette, and just staring into the air. I always wondered what she was thinking about. My grandfather had owned a supermarket where my father, my uncle and aunt had been running with him since they first opened. I remember walking the streets of Wynwood, Miami, around the block under the care of a local black drunk that will help my father at the store. These days were much different than today. Every where you went had that smell and look of the early 80’s, the clothes people were wearing, the tv commercials, the tv shows, the cars, the music, the faint memories of a time where no one used mobile phones, the interent didn't excist, Christmas specials still meant something, and most of all that feeling that everything will be alright. When i was finally in my mid or early 20’s, its when she started having her first episodes. My father will habe to call the police so they can take her in an evaluate her. Eventually she became 100% crazy. Why? She is such an amazing person, a beautiful soul, she didnt deserve to become sick. I guess we are all programmed differently, i still love her, but i will always wonder, why do peoples brain stop working.