I think “It was fear that kept me here” is better where it is than replacing it with “lesson three.” Fear did keep Luke there, after all. Fear that the Jedi have done more damage than good and need to die out (at the height of their power the Jedi created Darth Vader), fear of facing those he had failed (admitted as shame in the Ben flashbacks), fear of his own creations (it didn’t scare him enough then, it does now). His belief that his self-exile is a penance and a self-sacrifice for the greater good means it’s not exactly “cowardice,” but it all still comes from a dark place of fear, from a certain point of view.
Luke’s main thing though - why he isolated himself, why he cut himself off from the Force, why he wanted the Jedi to die, why he wouldn’t face Ben again - was shame. Luke says that very explicitly.
“It passed like a fleeting shadow, and I was left with shame. And the last thing I saw, was the eyes of a scared, young boy whose master had failed him.
But also, Rian Johnson took a lot of care and effort and attention when writing TLJ to make sure Luke wasn’t being a coward: https://comicbook.com/starwars/news/star-wars-the-last-jedi-luke-skywalker-coward/
Even if we can sit comfortably with the retcon, it still feels very much disingenuous to the character. And, if I’m being honest, pretty insulting to Rian, who worked very hard to honor a legend both in-universe, and out of it.
All of it for one sentence that’s ultimately throwaway…
I definitely want to keep Rey’s lessons on fear; I just think we can do that without dishonoring both Luke and Rian. We don’t even need “Lesson three” to do it; I just think it would be a nice touch.
EDIT: I’ll post some mockups later tonight, to show how it would work.
EDIT 2: Congrats, boys and girls, we’ve hit 400 pages! Dear god, that’s insane…