Edit: I looked at What are some ways to get to know your characters? and while I noticed similarities, I think that question asks in broader terms about what tools can be used for developing characters. I tried to narrow this question down to specifically the Myers–Briggs method, it's usefulness and limitations.
For a while I've been fascinated with the different personality types, studying the letters, function stacks, and how they play.
I've done tests to find out what types my characters are and spent hours reading up on that particular type, how that type thinks, their work habits, relationships, how they react to stress, whatever is available to find online (for free mostly).
That said, I tend to come up with my characters first and then figure out what type they are. It seems the more I get familiar with my POV characters, the less they seem to fit any particular type. Is this realistic or a fault in developing my characters?
I'll use my soldier character as an example. I tested him and he fell in the "ENFJ" category. (Extraverted, intuitive, feeling, judging) The more I read up on the type, the more I realized this type "can't" be a soldier. I put "can't" in "" because I'm sure there must be real life exceptions, but internet research is pretty limited, so I can't go 100% sure one way or the other. Long term wise over the arc of the series this type does appear to be the closest fit for the character and his development. Though early in the story he has his "mask" so it may be hard to type him with that mask on.
But then I noticed my character also plays up an "alter ego" or "work personality" (aka his mask) as a way to shut out his feelings and keep focused on his surroundings, and help achieve his missions/ battle tactics as a soldier.
Is this a bit unrealistic?
I decided to test my character again (factoring his work personality, the mask he puts on, how he carries out his actions rather than how he feels inside about what he is doing) and came out with an ESTJ. An ESTJ would be a more fitting type for a soldier, but he still has contradictory traits that make him swing between that, an ENFJ or even a possible ENTJ. (he does want to believe in abstract stuff, thinks towards the future, but because of a rough upbringing with his first father figure and a falling out with his second father figure, he shuns such beliefs initially and favors the belief to show fear (or emotion in general) is a sign of weakness.)
I'm wondering how much can I/should I rely on the Myers–Briggs system? Are such contradictions natural and realistic? I see myself as a contradiction being unsure if I use T or F as my dominant, swaying between INFP and INTP. I tested my own "work personality", the mask I tend to put on at work and came up with INTJ. The description of an INTJ doesn't fit me quite, but I can see things I can relate to, even more so when I read up on an INFJ. I notice I have a stronger judging preference at work than I do at home. At work I can't stand clutter, inconsistency, like to complete tasks, but at home I'm the opposite.)
Considering my real life example vs my character, is it that unrealistic for my character(s) to not fit cleanly in the "box" or do I have major work ahead of me to sort out my characters? (and perhaps myself in the process?)
Or do you make up the characters and if there are contradictions, you just let it go and try not to worry about it too much? (and that being what I need to do with mine?)