My best friend is an ISFJ. This type has a very strong introverted sensing function. Just as an example, he bought Starcraft 2 and was installing it. He mentioned to me that it was continuing upon the old story which made me laugh. I thought, "They're continuing a story from 13 years ago? Who the hell is going to remember that?" Well, he did. So to his credit, Si is something I marvel at. We do occasionally get into arguments over something. This is when I reach conclusions that have no solid basis in fact. He makes me explain how I derived a conclusion and what evidence it is based upon. The thing is, with Ni, the evidence I use isn't complete. It's a combination of several hints that cause me to make a stab at a likely explanation. He never sees how this is possible, because until it is proven, who is to say. I usually end up pointing out that he does this very same process in every day life; that the things he takes in as sensory inputs are really just perceptions, "hints" at the reality of things. He takes it for granted a chair is there when he sits down, but who is to say it's there until proven. He considers solid sensory inputs as proof. I end up agreeing with him to an extent that yeah, many things I believe will never be backed up by sensory facts; however, if I can reach a conclusion and there's a better than 50% chance that the conclusion is a correct one, I can act upon that conclusion in advance of knowing for sure. Therefore, it's a benefit to exhibit this quality because I believe that my hunches are perhaps 60% accurate. As long as the risk of being wrong isn't too great, then acting upon my hunch grants me a benefit. Investing is where this quality has come into play the most for me, but it's a fairly difficult endeavor as far as the discipline is concerned. Hunches are great in investing, but discipline is greater.