Maybe I've been a little misleading with my explanation of Ni. It not that I can't articulate where I draw my conclusion, it's more like people will rarely understand the validness of it, causing me to go through lengthy monologues so they can understand a concept they don't see as reliable (except my INTJ friends).
I had a friend (ESFP) ask my opinion of someone we had recently met. I replied that he seemed like a creep that was lying to try and impress her, due to his tone and the arrogant look in his eyes, and probably some other key things I don't remember. She got slightly offended and said that she didn't think my inference was well grounded, as well as "You're not psychic so don't judge people".
Needless to say she pursued some kind of relationship with him and discovered he was indeed arrogant, a liar, and a creep. She still doesn't believe that my way of interpreting people by things other than their overall appearance and what they tell you is a legitimate way of interpreting people.
Not the best example but I think it touches at the point I was trying to get across. Also, because I had to type all of this to explain the concept illustrates how I conversation about my Ni usually ends with people looking at their watches and finding an excuse to leave.