However, Si and Ni are the same in terms of the type of cognitive task they perform, which I think is what OMT was alluding to.
I think many people (especially INJs) underestimate the similarity between Ni and Si, because I think Si in general is very poorly understood and given a lot of inaccurate descriptions by people who think SJs are all just mindless rule/tradition zombies. (This manifests itself on the forum in terms of ISJs mistyping themselves as INJs being the most common self-typing mistake.)
VagrantFarce already explained this better than I can, so I'll reference his post here:
Also I agree that some of the definitions given here (namely by INTJs) are blurring the line between Ni and Te when they talk about "choosing the most effective way of getting things done", etc. Ni is a perceiving function so it's not making any kind of judgment about anything except the way meaning is interpreted. Ni might see a lot of different ways to look at a problem, but it can't pick the most effective/applicable one without help from Je.