i think i switch personalities all the time. there's serious irm, non serious irm, cranky irm, adorable irm and the list goes on for every trait and I can pretty much guarantee i'm a different person throughout each one. so if yous all have same personality through that then yous all fucked up.
writers boldly develop them, somehow, while somehow being able to keep them on a short leash. something i'm too often paranoid of attempting, as i question my strength to be able to hang on to it. i do have a stable of actors for my images, but they're just shapes, i haven't really tried to develop much in the way of personalities for them, the way good sf writers and experienced rp gamers do.
When I'm off my meds I display all three symptoms of schizophrenia. I think the age regression factors in a lot in how I come off to other people. But as for multiple personalities, one of mine is an Irish gentleman. That's only when I'm not on my meds, though.
Their is limited truth in what you say, particularly in mental and stress related illnesses. Conditions such as diabetes may have been prevented (rather than cured) if your early personality prevented you from over eating the wrong foods. I am not alone in thinking that cancers may include an element of stress related causes. Diseases and viral infections may also have some degree of prevention by a strong healthy personality leading to a stronger immune system.
many physical illnesses are exerbated by psychological stress, and amiliorated by avoiding it. this has highly motivated me to avoid such stress as much as humanly possible my entire life, and of course i have sacraficed many potential economic advantages in order to do so. some poeple choose to be offended by my choosing to do so, some misinterpret it as an unwillingness to exert effort, which it is nothing of the kind, but rather an unwillingness to risk otherwise needless stress. can't say as i always succeed even at that, but it is, remains, and has always been, one of my personal priorities. well i've made it these 73 years, which i realize is no longer unusual, none the less, i give stress avoidance a very large share of credit for having made it this far.
i seem to be no good at developing ANY personalities, let alone more the one. writers and actors, yes it is an art. i'll stick to illustrating the concepts that entertain my imagination, which, for better or worse, are something other then genuine people personalities.