Man, this is a great thread.
I was thinking about my Fi, and I definitely don't trust it at all for actually influencing my behavior. Anything Fi related immediately gets stuck in my Ti without really realizing it.
I'll be thinking, how did that situation make me feel? I'll get an answer, but I would never dream of actually behaving on that feeling in the moment. But it is there... and I feel as if it can only consciously influence my decisions if I think about it long enough. In the moment Fi? It's pretty much like it doesn't even cross my mind as an option for behavior.
Just trying to understand that... I find myself 'realizing' I don't even have arguments for defending my Fi if it would ever fully surface. How bad is that? I can definitely see how anything like this would throw off somebody who expects Fi for the base of a friendship.
I have a somewhat developed Fe, at least good enough to make good Fe conversation if it strikes me as important... but it's still weak enough to miss many highly developed Fe's intentions and motivations if I don't remember or care to look for it. Man, what a shame for us INTP's that most of the world feels consciously...