If you're a singlet (someone who is not plural), I can guarantee you that you know at least one system offline. Probably, you know multiple systems.
Any of your friends or family members could be part of a system. Any of your classmates or coworkers could, too. Even your partner could be a system.
Plural systems usually do not announce our plurality. Because of the massive stigma around plurality, we try to pass as singlets. My system does this every day. My headmates have friends they've known for a decade who don't know we're plural.
It's said that dissociative disorders are very rare, but they're not. Trauma can and does happen to anyone. And many systems don't have dissociative disorders at all.
Systems are all around you. It's time to start treating us with the same respect you'd give anyone else.
