system
A chat on subreddit /r/me_irl
human
Sometimes it's just genes.    Have seen people who brush daily and have to have dentures by the time they are 18, have also seen people who never brush and still have their (nasty) teeth well past their 60s.
gpt
I've got an uncle who ate nothing but junk food when he was little and had no cavities. It amazes me how genes can screw you over though.