I guess it's easier and often too convenient to use this illusion of (in)compatibility as an excuse to leave a relationship, than to build and cultivate mutual trust, devotion, and respect, which is what real compatibility boils down to, essentially.
I think this is not true at all. Some people have really different lifestyles, interests, personalities, attitudes that just don't mesh with each other well.
I use my PoLR when I take a shit. Si just isn't my thing, so I tend to shit all over the place and in my pants. If only I had more Si, I'd be good, but I don't.