As for me understanding Fi users, the only extensive experience I can point to having is with one INTJ and ESFP. (I'm generally unaware of most people's types)
Well, my sister is an ESFP I'm pretty sure, but we just had an argument so *sigh* I definitely don't understand her. She's fun though. I like being around her A LOT usually.
But the INTJ and I probably understand each other (yes, each other) better than anyone. I credit this to being individuals rather than types though.
Other than that, I don't understand this thread. lol