Here's a little chart.
View attachment 12102
For anyone who doesn't know socionics:
Ni = white triangle
Ne = black triangle
Si = white circle
Se = black circle
Ti = white square
Te = black square
Fi = white L
Fe = black L
I can talk about this, but I'd have to get into my weirdo bizarro interpretation of Alexander Bukalov's Model B in socionics, and I still don't know if I'm understanding it correctly after all these years because I haven't bothered to try digging through automatic Russian translations full of gibberish. Instead, I just test the theory by observing it happening in reality, and it's extremely accurate, the best thing I've ever seen so far.
So, nobody would agree with my technical explanation of why these mistypings happen, because most people here aren't using Model B. But oh well. Here goes. I expect a few people's brain cells to fry as they struggle to understand a completely different system in a completely different universe - or, alternatively, everyone will just get bored and skim through it. Sorry.
Some of these mistypings occur because these types actually have a particular information element in common, according to this model. For example, an ISTJ can be mistyped as an ISFP because they are 1. both introverted, and 2. both have +Si/-Se. In the chart, it shows a plus sign with a white circle (Si), and a minus sign with a black circle (Se) - both in the same little box, and each element can be either on the left or the right. That's assuming you can read the tiny little sideways text with the type names beside each rectangle. ISFP is in Alpha, and ISTJ is in Beta.
I've mistyped an ENTJ as an ENFP because they are both extraverted and they both have +Ni/-Ne (+white triangle, -black triangle). When I meet an ENTJ, I can tell that they have a weakness of +Si/-Se, and that weakness is very visible to me, and I like them because of that weakness (since +Si/-Se is one of my disvalued functions) - I feel like I could be strong and protective towards them, and I feel like they need me to give them food, initiate physical contact, and whatever else sensing does. (Yes, I know I wrote a thread elsewhere that said if I retype my boyfriend again, ignore me, but...)
Sometimes I can only see very general things about a person. I have a coworker who I really get along well with. I think he is 'Not Beta,' but I don't know what quadra he's in beyond that. (Your opposing quadra is one of the easiest ones to type people in. The quadras next to you are harder.) He is definitely irrational, and logical. So he could be an INTP, ISTP, or ENTP. He told me that he was in a car accident when he was young, and it gave him brain damage and altered his personality. He said he used to be more of a bully to other kids, but after the wreck, he became quieter and more timid. So this brain damage may be one reason why it's hard for me to type him.
For some reason, a particular function might really stand out to you when you interact with a person. You might be only able to see that one thing really clearly - not just the functions like Ni, etc, but also the extraversion or introversion, irrational (perceiving) or rational (judging).
That whole chart would make absolutely no sense to someone who didn't already know socionics. I won't explain why it's set up the way it is, because I don't necessarily agree with their rationale, and I wouldn't mind if they just had all the functions lined up left to right instead of in that rectangle. But, here is the order the functions go in. You start at the upper left:
1 2
4 3
6 5
7 8
Don't ask. Just don't. They say they wanted to make it so that the upper half 'spins' clockwise and the bottom part 'spins' counterclockwise.
Another thing that affects your ability to type someone is the drugs they use. If anyone I know is using psychiatric drugs, I find it almost impossible to figure out what type they are, because drugs drastically change all of your behavior. I have a coworker who *seems* extraverted (but might be an introvert who's really talkative and outgoing because of the drugs), and seems like some kind of sensor (but which one of my neighboring quadras? or my own quadra?). He really likes the two ESI girls and he also liked a girl who I thought was an LSE or LIE, but who could actually be just about anything because of the horrible wrongness of all my mistypings. But I try to figure out what type someone is based on which people they are most comfortable with. I really like working with this person and he seems to have problems with the same people I have problems with, so I suspected LSE for a long time, but I just cannot make up my mind about it. If he weren't on the drugs, I'd be able to see his true self much more clearly.
Someday when I have infinite free time and infinite free money, I'm going to make my own personality type test, and it will be 100% accurate the first time, every time, for every person. Until then....