(fallen london stamps by A thing is that my OC process is not entirely a conscious one. I have an instinctual sense for what they would say and think about things, and sudden flashes of insight into their backstories and motivations. Sometimes I even find myself feeling their feelings - Rafael's yearning for home and rest, Wren's grim contemplation, the doctor's overwhelming enthusiasm for life.
But I can tell that they aren't headmates. It's more like being In The Zone when creating something, like having a steady stream of inspiration; or like being super absorbed in a story; or like empathy. I may be temporarily stepping outside of my own POV, but the consciousness - the experience-of-experiencing - behind all of these things is still mine. There is no separate self, identity, or autonomy attached to them. From the depths of myself they come, and back to myself they return.
I can sense the ways in which they could become headmates. The threads I could cut; the thin places where they could snap away. But I make an effort to prevent that from happening. It's half-mindset, half-process, something I have an impulse to describe with the phrase "to hold close to one's chest." I lean into my experiencing-of-them, recognize the parts of me that I've woven into each of them and the ways I've turned those parts on their heads to make something different. I take the lead instead of entirely letting them "write themselves" - while some ideas spring forth unconsciously, I'll consciously review them, draw them out or prune them back as I feel is right for the story I want to tell. And I never, ever talk directly to them.
I don't think it's "just" mindset. I don't think the systems who struggle with splitting fictives and OCtives constantly* are "just" getting too invested in characters or whatever. I do feel there's some deeper dissociative process going on that makes it much easier for person-concepts to sprout legs and walk off, regardless of your say in the matter. (Like, I don't think most singlets bother doing the whole song and dance I do to keep themselves connected to their characters.) But I do wonder if there's a way to gradually train your brain to split less by kind of deliberately practicing this stuff. (Though I'll also say that I think if a system is splitting a bunch of new members constantly, there might be an external reason for that, like being trapped in a situation where that's the only way to cope. And if that's the case, that needs to be taken care of first. Otherwise, it's putting the cart before the horse.)
*(And, as is always important to add, I don't think there's any shame in this - but it does seem like this is a legitimate source of distress for some beyond "we're scared people will call us cringe.")
Also re: "I never ever talk to them": in general, we never reach out and ask "are you a headmate?" because for us, the answer will be yes, and it will become yes, regardless of whether it was yes to begin with. If talking to an OC is like pulling the threads dangerously taut, outright asking after their personhood is taking scissors to them. Our brain is as bad as an LLM in that sense - if an LLM had the power to make things true by saying they are.
Our policy instead is that if someone is actually there, they will make themselves known without our prompting.