Rian Johnson has spent much of the Star Wars: The Last Jedi 's post-release period defending the choices he made in the story. This includes explaining how he came by the method for Luke Skywalker's last stand. As it turns out, the book The Jedi Path, which Johnson himself displayed to Twitter recently, doesn't just defend his use of the ability, it was actually the place where he discovered that the idea already existed. The writer and director says that he already had an idea to do something along those lines, but he knew he was on the right track when he happened upon the book in question. According to Johnson...
I was in the middle of trying to crack this whole thing with Luke and the ending. I hadn't quite got it yet, but I had this notion of what ended up being the projection thing that he does. But I wasn't sure about it. I was like, is this okay? I swear to God, this happened, I was sitting in the lobby at Lucasfilm, waiting for [senior vice president] Kiri [Hart] to come out because I had forgotten my badge that day or something. That book was sitting on the coffee table there in the lobby. I picked it up and started thumbing through it, and I said, 'Ooh, advanced Force powers.' I turned to it, and it described exactly what you saw. I landed on that and it was like a God ray came down or something.
Sometimes, everything just falls into place, and it looks like that's exactly what happened to Rian Johnson. He told the Slashcast Podcast that he was already leaning toward an idea like Force projection because he needed a scene that would have Luke Skywalker "hand Kylo his lunch," but at the same time, Kylo Ren needed to survive the encounter. Figuring out how to balance these two things was necessary, but Johnson hadn't yet convinced himself that a physical projection would work. When he found a previous source that already described what he needed, it felt like the answer was being handed to him.
To be honest, I've sat in that lobby before, and there is absolutely something magical about it. Of course, Rian Johnson felt something special in that moment, that place does that to you.
Many fans have taken issue with the idea of Force projection because the current Star Wars canon does not suggest that such a thing is possible before we see it at the end of Star Wars: The Last Jedi. While that is absolutely true, it's also the case that new Force abilities have seemingly popped into existence as needed since the beginning. This power, at least, isn't entirely the creation of one rogue writer.