I admit I didn't read all the walls of texts above (don't have the time right now), but I think Ni-base is characterized by uncertainty. If there's one thing you can be certain about, it's that you can't be certain about anything. This "feel sure about" sounds like a bunch of MBTI stereotypes, which originally discouraged me from even considering Ni types. In my experience, it's the types with weakest Ni that have a tendency to assume things will be this way or that way, or alternatively that they can't be predicted at all. The stronger the Ni, the greater the awareness of what can and what can't be foreseen with reasonable accuracy, and its lack of certainty despite the consideration of probability.

xIE aren't so sure that everything is going to go as it seems. They have to make it happen the way they want to. They take take all the consequences into consideration. Plenty of LIE descriptions describe how they take calculated risks.
Ni-base are even less sure of it. (Unless I'm completely wrong about Ni and being one, which is a possibility.)