seol is INFJ and jung is INTJ! i think they both heavily rely on introverted intuition, which is the ability to be perceptive and see patterns in people and situations and this is how they analyze the world around them. they are especially sensitive to details that others don’t often notice and they can almost accurately predict the outcome of certain situations. there are often times when both of them just sense when something is off (like when seol senses a weird tension at the english academy or when jung starts to notice his dad’s behavior slightly changing way before he deduced it because someone was reporting on him to his dad) and then have a lightbulb moment of what exactly is amiss. they tend to find symbolism in what happens to them, like how jung is strongly against repeating cycles which we can see in how he analyzed inho’s life choices so far and gave him according advice. where i see them differ though is of course with seol being F and jung being T. seol uses extraverted feeling very blatantly as she is someone who values the good of the social group or the family over her own needs time and time again. she is always reading people (as jung does, but for different reasons! as we learned time and time again) to understand their mood and personality, to the point where she doesn’t even realize she’s doing it. but that’s how she always has interacted with others and she has a strong urge to take care of others’ needs even to the detriment of herself, which she thankfully improved on. for jung, i specific example where i identified that he uses extraverted thinking was when he was describing to seol how he calmed down and taught areum. the way he explained his method was so systematic and was similar to how coding/computer programs work. i often notice people with strong extraverted thinking are concerned mostly about what is most EFFICIENT. they can organize people and rule out strategies that aren’t as efficient, and they aim to get stellar results without doing any useless work. we can see this at play in the scene where he has a group project with jaewoo in season 1, where he suggests cutting down the number of articles they read and removing unnecessary information as they can get a good grade by focusing on the quality of the content. anyways, this was my reasoning from what i know about MBTI. i’m no expert but this is just my take from my previous analysis when i first read through the story years ago!