What is it with the Dark side, anyway? I came across the argument, somewhere, (possibly The Hidden Truth Behind Star Wars) that the Force, apparently, is trying to come into balance, because both the light and dark side are necessary.
A lot of us are used to the idea that it's balance that's important, not an extreme of light or an extreme of dark. Actually, if there ever was a balance in the Force, what would it look like? If they weren't busy fighting each other, what would they be doing?
Maybe these questions are actually answered somewhere, just not in the Star Wars movies.
Now I'm coming to a thing that amuses me. There have been some jokes about the Sith destroying planets and getting their own death moons destroyed. You'd think they'd learn not to build such big targets.
The Jedi have had their own vulnerable points. Anakin killed a whole school of Jedi children. Apparently Kylo Ren also killed a bunch of Jedi school children. Luke was running that school. I figure Luke left the scene not just out of grief for the children (Padme was so ready to forgive Anakin for the murders he committed that you start to wonder what it is with children's lives in the Star Wars universe. It's nice to think that Luke, at least, might have grieved for them. Leia and Solo just grieved for Kylo/Ben)
So, the amusing thing is that, after two whole Jedi schools have been murdered, Luke, unlike the Sith, learned his lesson. My theory is, he got a different idea about how to school the Jedi.
He disappeared, but left a map. Albeit a difficult to find and read map. But a map of where to find him, nonetheless.
Maybe he figured that bringing all the Jedi children together in one place where they can be conveniently murdered is not such a smart idea. Given that the Force is a bunch of midichlorians (I think I've read about one Star Wars book, but I'm not a fan of the midicholirans idea - and why are they even called that?) permeating life throughout the galaxy, maybe there's another way to communicate and train the potentials (yeah, I'm borrowing the term from Buffy). Maybe that's what Luke has gone away to think about. Besides, if he's found and killed, he can't achieve anything at all; the Sith want that map, they want to find Luke and they want to kill him.
If he's far away, the Sith can't sense his presence in the Force - apparently. We know this because they haven't found him and can't sense where he is. We also know Luke has at least three ghosts to help him. Obi Wan said to Darth Vader, "If you strike me down, I will become more powerful than you can possibly imagine." We're still waiting for that power to manifest, although it could well be something the midichlorians are enjoying and we won't see it in this dimension. There's also the ghosts of Yoda, and of Anakin himself. With their help, Luke could be secretly training the next generation. By remote control.
This could be why Rey catches on as to how to use the Force unnaturally quickly. There have been complaints that she's a bit of a Mary Sue, that she does everything too well, too quickly, too easily. That doesn't worry me too much. Some of it she learns from Kylo Ren when he tries to use the Force on her. The mere fact that he tries tips her off on the fact that it can be done. And then his efforts to see into her mind allow her to see into his. (I've got a feeling that I've read similar scenes to this before, but I can't remember where. It could be just a standard part of telepathy stories.) If there has to be a further reason why Rey is so quick to learn the use of the Force - apart from already having begun to learn it when she was very little - this could be it. Luke is somehow using the Force to teach her along with the other potentials. This probably requires a lot of concentration, which is another reason he might want to be by himself.
Now we have to find out whether Rey has broken his concentration by arriving (but he may have sensed the death of a friend earlier anyway) or whether her arrival (assuming there was always going to be someone like her who would turn up) triggers the next stage of The Plan.
Of course there's a Plan. What, you thought the writers were just making it up as they went along?