What you are hearing from others about Fi, is a function that is presented in a way that it only CAN be presented. It has nothing to do with objective value or strengths, but rather, a sense of being. It's...you. But, to try and give you a "strength" at least in a way you are requesting of it, I can tell you what it has and always will do for me. Well let me just say, that this is something I've felt long before getting into personality type, and is something I assume to be attributed to Fi, though, for all I know, it might not be. But, one thing I highly relate to with the ENFP typing, ESFPs do this as well, is that they appear to be the sorts of people that can just "go". At the drop of the hat, they are there. There is little structure in their lives in the view of many of those around them. But here's a secret, there IS a structure, and there IS an organization. There IS something holding all that external crazy together, and it's something no one ever sees externally. You
can see it, if you know what to look for, but to the average person, that structure is absent.
What I'm talking about, and what I've always known and felt of myself, is that amidst these fun adventures I absolutely feed off of in the day-to-day, the ideas, the creativity! The glue, is me. What I mean by that, is that I have this inner understanding of myself. I know who I am inside and out, how I feel, what makes me tick, my insecurities, how they come out in my actions and words, my experiences and how they made me feel, how I've then grown from those experiences, or didn't. My hopes, my dreams. How those dreams guide me and where they even stem from! I know how the people I've met have shaped me in ways, emotionally and mentally, that some people wouldn't consider examining. While I continue to find new bits of me each and every day, and in my times of introspection (which I do quite often), each day I have the confidence that what I know of myself in that given moment, is the fullest I could ever know myself, with no rock unturned. And yet, I continue to surprise myself as I jump into new experiences and meet new people, that NEW information of myself, a new crevice has just been discovered, and it's always such an enlightening and satisfying experience. It's never unsettling or jarring for me.
So! to return to that strength you seek of Fi. For me, the strength of Fi comes from how deeply I feel I know myself. It is such a solid and confident place, it is exactly what allows me to take those leaps and jump to new heights and dream those fantastic dreams. THAT, is the internal structure I speak of, and what I have always known as true in my life. I may not know what's around the corner, what will happen to me in this situation or that, or even if I will like it, but it doesn't matter, because so long as I know of myself is true, and it FEELS true (it really is an inner sense of just "knowing") then whatever happens to me externally, whatever is thrown my way, good or bad, can do no more harm to me than I can do to myself...if that makes sense. I genuinely believe I am the sole gatekeeper to my own demise and downfall in life, and so long as I do not allow that to happen, so long as I make that decision not to step towards that direction, I can just keep on smiling and keep on living life to its fullest.