Hi,
Like others here, sometimes I either don't plan things out enough in advance while at other times I find that I get so worked up about trying to figure out how to do something, that I end up getting burnt out on a build before finishing it.
Right now I still have a 1/400 model of the Russian Pre-Dreadnought Potemkin from at least 8-10 years ago that I still have not added my photo-etch railing to, because I'm not 100% sure what the best way to add it would be (especially since the PE is from a generic set and not specifically made for the kit).
Similarly I also have a ~1/300 scratch built/3D printed cruise ship that I haven't finished off because I didn't give enough thought initially to how to complete it so I've just let it sit for a few years, playing around with a couple different ideas on what to do next.
Pat