ISFP: Fi > Se > Ni > Te
ISFJ: Si > Fe > Ti > Ne
ISTJ: Si > Te > Fi > Ne
For the sake of privacy, names have been changed. I'll call ISFP Marie, ISFJ Nora, and ISTJ Kris.
Nora and Kris have a history of tension, especially when it comes to making plans. Nora has auxiliary function Fe which is related to valuing and maintaining group harmony (even if it overrides her personal preference). Kris is Te auxiliary which is related to maintaining objective rules/organization/planning. After looking at their function stack I suspect this difference is the main reason they have such a hard time planning things with each other. Similarly their tertiary functions are opposite - Kris's Fi helps maintain personal values/authenticity while Nora's Ti deals with her internal logic. Add to this that they both have Ne as their inferior function which is often the one that comes out during stress. Ne deals with making connections about the external world and can manifest as "suspicion" or doubt about meanings. So when Kris and Nora try to make plans one is trying to uphold an objective set of rules that aligns with their personal beliefs and the other is trying to create/maintain harmony that aligns with their inner logic. Both are suspicious and doubting the meaning of each others communication, potentially drawing conclusions or making connections that aren't really there and "reading between the lines" (I have witnessed it first hand haha).
Comparing Marie & Nora
Fi dominant Marie leads from a feeling of authenticity (does this align with my values?), auxiliary function is Se which relates to seeing the world as is and appreciating via senses (she's very nature oriented, likes fancy things, good at art and diy). Ni is about how you interpret the relationship/meaning of what you perceive according to your own internal perspective (like your own mental map), and Te is external organizing. Si dominant (Nora & Kris) lead from a place of "what's familiar, what works - tried and true, tradition, and remembering details of the present moment". This is probably why Marie seems more open to change or more independent minded than either Nora or Kris, and why she might perceive the others as controlling/rigid. Nora is much more family and business oriented than Marie. While they're both very reserved, often altruistic, and very perceptive about details in the present moment (like cleanliness, fashion), Nora adheres more strictly to tradition and family values, and seems more rigidly tied to those values. Her choices very often consider "what will others think", while Marie is a "free spirit".
I recently went on two separate vacations to the same destination, one with Nora and one with Marie. The difference between these two people in the same environment inspired this analysis. Previously I was certain that both people were "F" types (but on the fence about the J/P dichotomy), but how that F shows up according to the function stack is very different (and it I think my experience reflects this). Nora (Si > Fe), albeit less familiar with the vacation destination often seemed uneasy or uncertain about trying new restaurants and activities, but she always went along with the group if we expressed that we wanted to do those things. Every morning she asked, "what's the plan?" And I'm reluctantly accepted "we'll see, were on vacation" (we probably caused her more stress than we realized).
Next trip was with Marie, who I had typed as an F, but did not consider the function stack. I actually assumed her and Nora were the same type because they have many similarities, despite a few obvious differences I could never quite put my finger on. I assumed Marie's judgements were Fe based, so I was surprised when she made several decisions that I felt were inconsiderate. A couple mornings during our vacation we discussed our plans for the day, and I made sure to communicate our whereabouts so we could meet up and go for lunch or do activities together. Several times (multiple days) I sent messages to check where Marie was only to discover she had gone ahead with a different plan (already had lunch somewhere else, decided to go somewhere different or do a totally different activity) and had not communicated that to me. We ended up doing many more things separately than together. Technically Fe is not in her stack despite being F (although I still suspect it's a strongly developed shadow function for her). She makes decisions first according to how she feels, whereas Nora would make the decisions first by what's familiar to her supported by how she thinks the group feels.
Interestingly, I realized that Marie (Fi > Se > Ni > Te) and her husband (married for over 45 years) share the same cognitive functions but in different orders. He is INTJ: Ni > Te > Fi > Se.
Nora (Si > Fe > Ti > Ne) and her husband (who I suspect is ESTP: Se > Ti > Fe > Ni), also married for many years, have inverted functions of the same type.
I suspect Kris's (Si > Te > Fi > Ne) husband is an ESTJ: Te > Si > Ne It's interesting to note that if I'm correct then they also share the same functions but in different order.
Maybe I should become a match maker based on MBTI? Wouldn't that be a grift.
After doing this analysis I feel like I have gained some insight on these three people and their chosen behaviors. I think the most important part of learning MBTI is not whetherit's accurate, but that it helps people gain empathy for ourselves and others through imagining and describing how other people might think and make decisions.