I'm an MBTI nerd, lol.
People always find it strange that there are so many INFJs online when it's supposed to be rare. But we are hardwired to appreciate the process of sorting other people's personalities. Drawn to it like ESTP's to a car show.
One thing that should always be kept in mind is that it's a self-reporting test. That means how well you know yourself matters. And the tests can only state how confident you are of a given function.
I'm not a fan of the varying degrees of agree/disagree, but I thought it was accurate.
That's just how certain you are.
So MBTI is just the instrument (test), but the underpinning is Jungs theories on cognitive functions.
The functions hold up well, while the test itself can be kinda iffy (in my opinion, the questions are too obvious, and they carry bias from the test creators, but nevermind that).
Dr. Dario Nardi (of some university) did EEG studies comparing people with specific personality types to different ones. He found an 80% correlation in brainwave patterns depending on one's type.
It's good to think of the types as broad categories that explain a person's process of thinking, rather than the results arrived at.
I've slowly shifted closer to Architect over the years (now only two points away). I feel like it's the upgrade to my personality type.
Well, according to the system, people don't change their personality types.
But there's a process of growth where people begin to expand their abilities with their weaker functions. If a person develops well, they become more balanced over the course of their life. With age comes wisdom and all that.
On the other hand, if people don't develop well they can stay stuck as the product of their dominant function.
Also, big life stresses can fling people back into what they know. And trauma can cause some to avoid certain areas of growth altogether.
Personally, I'm more of a "looper" - leaning on my dom and tertiary functions, because I've found the auxiliary to be unreliable (dealing with humans, so of course it is).
I think what I like about the system is that it provides a framework for people to talk about their differences without all the vagueness of typical self-descriptions. It helped me understand my mother better than I did, and it helped me stop dismissing people as stupid if they weren't always thinking several steps ahead.