I definitely have "serious" questions concerning Fi (Fi is an interesting animal) but it's been my experience that Fi'ers really don't want/like those serious questions - and sometimes the dialogue becomes delicate, stressful, or even heated (both IRL and on the forum). So, if my question fits the "uncomfortable" category, just politely let me know and I'll skip on my merry way. I come not to stir up the pot, but to understand the animal that is Fi.
I'll ask it bluntly: Why do you guys not clearly express what Fi is feeling/thinking? If you're upset, mad, angry, disappointed, frustrated, feeling ignored/betrayed, etc. - why not just tell the other person exactlly what those feelings are, which then gives that other person something tangible to work with. Basically, my confusion with this part of Fi is that if you never voice what's going on inside (plainly, clearly), then you'll probably never get any results that resemble what you're hoping for/wanting.
If I could draw an analogy, it'd be something like this: The Fi'er
really, really wants a shiny red sports car for their birthday (or a penguin, or a pony, or something along these lines). When someone asks you, "What would you like for your birthday?" (cuz they want to get you something you'll really like), you just say, "Ehhh, I dunno, a gift card"

And, so, you end up getting a gift card and you feel upset or kind of sad that you didn't get the sports car. Well, you didn't get it cuz you didn't ask.
Or, the Fi'er wants to spend time with someone they love. And they talk to the person they love on the phone and the person says, "Whatcha doing tonight?" And the Fi'er says, "Heh, not much."

So, the other person thinks, "Hmmm, OK, they aren't doing much and I'd like to see them, but I know they like their space and I don't want to impose, so I'll just leave it at that and maybe see them next week sometime." Then they say, "OK Fi'er, good talking to you, we'll catch up next week." And then find out later that Fi'er was very upset and wanted them to come over.
Why doesn't Fi'er just say, "Yo, check it out. I want a red sports car for my birthday and I also want you to come over tonight and hang out with me cuz I miss you." Straight up. Tell it like it is. Done! Finished! Wish granted. It can be so easy, so simple. But, instead, you never voice these Fi desires and so the other person..........never knows what it is you wanted. Inevitably, this will cause feelings of hurt and neglect and "he just doesn't know me".
I've heard 2 different reasons for this "holding back": 1) It's hard and/or uncomfortable to express. 2) Fi'er doesn't want the other person to do something for them "just because they told them they wanted it" (thereby "prompting" the action); instead, Fi'er only wants things to be done for them without prompting, completely of the other person's free will.
If I compare Fi to my own Ti, then yeah, I can relate that it's sometimes hard to express "complex thoughts" into mere words (and some things get lost in translation), but if I really want something, you better believe I'm coming out with it eventually.
Why Fi'ers? Why?
Again, if this question/probing seems in any way hostile, critical, or uncomfortable, just send me on my way and I'll leave.

I think it gets touchy sometimes and that's not my intention here.