This might have been said before. Just sayin' it again.
From the Lenore wiki:
Our functions are orientations, lenses through which we view the world. All of our lenses are imperfect.Ni is a way of knowing (or at least thinking you know) that bypasses reason, facts, evidence, the expected or intended interpretations of signs, or anything you can point to, simply giving you an awareness or belief that seems indisputably true to you, period.
Although, this raises a side question, too. Should we think of the functions themselves as archetypes, and our preferences as orientations toward those functions? That is, perhaps Ni captures knowing without facts or logic, and an Ni-dominant is oriented toward Ni, but has an imperfect use of Ni?