On the paper it says the one uses Fi and the other one uses Ti. You can go further and say they both use it but with difference strength.
Yoou can now start analyzing what Fi and Ti is about but I think you have to live it to know it. There was a time in my life, I smoked a lot of pot and thought of myself to be the mutual ladies men from the neighbourhood. I really never figured until I quit the mind altering thing that I am not.
I am not nearly capable of seeing so much interpersonal things going on, on a virtual level of existence I have just not entered. I nowadays get through my INFJ girlfriend alot from this VR. She has Fi according to socionics and thats what I believe in and that Fi is a beautiful but rare thing at best.
I myself get glimpses at it from time to time and it brings me insight, like a total new view on things and it helps me alot to REALLY understand people.
For example a long time friend of mine, I always thought he is a very rational guy. My girlfriend got to know him after I knew him for like 15 years and she told me that he is a huuuge feeler. I declared her for being insane, nevertheless I listenend to her story. And I tried out what she told me on, how to deal with him. The result was devastating for my belief. He openend up became ultimately personal and my relationship to him reached a new closure. A closure far to close for me in that case...
I myself am hurt and sad very often, because my INFJ blends in that Fi capability and shows me a way of interpretating human things that is totally alien to me but makes sense and is experienceable.
I dont want to think further because I get sad, when thinking about what I miss, I just want to say a polite fuck you to all ENFPs and tell you to value what you have.
You will never build electrical circuits THAT big like I do in that less time !!!!!