I both get Si and don't get it at the same time.
I actually relate to it fairly well, however I know I don't actually work and think in the way that Si does. Proof positive of this is when I try to mirror the methods in which Si dom's try to, I get really stressed and do poorly. That said, I can work well along side of them. For me to actually do it though, it's just too... rigid? It's difficult to explain. It doesn't allow me to make in the moment adjustments which are essential for me getting to where I need and ultimately making good decisions. It's essentially a difference between process oriented, and goal oriented. I am much much more goal oriented. Process is important, but insofar as it doesn't hinder towards the goal. As such in some cases I'll heavily focus on process, other times I won't at all. This shifting in method tends to confuse Si user's, as they see me being very chaotic with no pattern. There will always be a pattern to me, but if I try to explain it the response is usually along the lines of "...but that doesn't make sense", so I can be at a total loss to explain it. If the Si user is able to go "you know what, I don't get it, but what you do seems to work, so have at it!" we can get along quite well. I have a ton of respect and quite like a lot of ISTJ's in particular because of it. When that doesn't happen though, working together can be very difficult. With some I'd sooner chew a bucket of sawdust.
The major reason why I relate to Si is because I can be very process oriented at times. In particular when I start something new and realize I need to know it in depth. However, the exact method in which I do that is not how Si functions. It's very case by case. Over time I'll start distilling things down to a finer and finer point/method and the process becomes automatic, nuanced, and surprisingly flexible. Very unlike Si. Another part of is I don't relate to Ne even in the slightest, so that opposing pole leads to surface relation to its inverse by virtue of the fact that Ne does not compute in my brain.
The number one thing that Si can bug me with is when it refuses to accept a working method because it's unable to understand it for itself. The lack of "big picture" can annoy the piss out of me.