Or, if one comes down with some illness where he/she must be monitored at all times, I imagine that person would be more of an extravert because of needing to be around people? I'm not sure, sort of thinking out loud here.
I've actually been wondering about this recently... as recently past events have reared their head within my conscious mind and I have become aware of the fact that as a result of them, I have built a myriad of defense mechanisms. It's evident, now, in my apprehension toward relationships (friendships or otherwise) and the way I conduct myself in social situations.
I wonder if at the core, I could be an extravert. When I was a kid, before all this defense building started, I was excessively outgoing and chatty. When I take the cognitive function tests, they usually come out as ENFP though I test as an INFP.
Everyone has a core personality that can not be changed (however, severe mental illness onset might change it). Your type is a core to your personality. Once you develop your primary function, that will stay with you for the rest of your life. Whether or not you figure out what function that is a different matter.
What if they used drugs to the point that it changed them? I have noticed that many of my friends after they have recovered became someone completely different. Like they were not them anymore. At all even after years.