It sounds to me like you just lack discipline. Don't think of it as Fi, and don't think of ways to fufill this idea of "Fi". Don't think of it in any other kind of super abstract terms, just look at it as who you are and what you want to do, honestly and realistically. I've personally found that trying to explain and/or justify what we want/who we are/ect complicates things.
If, for example, long posts bore you, weigh the benefits. Is what you want to communicate in the long post ultimately worth the effort of writing it out? If yes, write. If no, find a better way to communicate the thought or find another thing you want to do and try it.
I find a good way to help make things happen for me and keep myself disciplined in important areas of life is to do rather than say. What I mean is, if there is something you want to do, make it your priority to begin doing it, and avoid talking about it to other people or fantasizing about it excessively. For example, if I wanted to paint something, I would get the neccesary supplies, set it up, and begin working on it. Even if I was very excited about it, I would not talk about it to friends or family untill after it was complete or very close to complete. Any time I have talked about some project I wanted to do before I actually worked on it, working on it didn't seem as satisfying or engaging as if I just did it and didn't bring it up. I think what happens sometimes is that talking about an ambition or goal enertains your ambition or goal just as much as actually completing it can, which is why I avoid enertaining my goals in any way other than completion. And when this happens, you still end up dry, whcih is what I think you may be getting at.
I realize that thats all sort of my own personal approach, but play around with it and see how it works for you. The difficult part about these kinds of problems is they can be massively different from person to person, and thus require different solutions. I hope everything goes well for you.