How do I explain Si...
I prefer to do things that I already understand. I drive the same way to work every day rather than try to find "newer" or "faster" ways. The more I watch a movie, the more I like it. Nostalgia is an incredibly strong, and almost overwhelming feeling to me. When I go somewhere, the first thing I think is "Hey, remember that one time I was here with ___ and we did ___?" rather than make observations about the environment and look at what's there now, in the present (unless it is different from before. Then I will notice it right away). I play as Peach in Mario Kart because I always play as Peach, and I don't really like or even want to play as other characters. Umm... how else can I describe it?
Si is like a lens. When Si-users look at something, they see how it used to be, or how it's different than it was before, before they see what is there now. Si-users have a vast storehouse of memories and information that we refer to whenever we encounter a problem.
Having high Si means having low Ne, which means that the Si-user will have a strong preference for what is "traditional" or what they already know, but that their Ne will occasionally pull them towards the idea of novelty and spontaneity, which could be a positive or negative thing for them, depending on the circumstance. On the inverse, a person with high Ne who has low Si will be a person who prefers trying new things every time, but will occasionally feel a little tug of nostalgia to do something they used to do when they were a kid or something.
Hope that explanation was okay.