In the same movie, Yoda reveals to Obi-Wan that Qui-Gon Jinn has learned how to maintain his consciousness after death. At first it sounds like he knows the secret, then it becomes about discovering the secret together, which includes Anakin having to do a bunch of evil murderous things as Darth Vader to become 'strong enough with the Dark Side.' Of course, tragically, Anakin's mission to save his wife from death becomes the very thing that causes her death, which he'd seen in vision, in the first place. It's strongly implied this was Palpatine's own master, who he murdered in his sleep.
In one of the movie's strongest scenes, the future Emperor relates the story of Darth Plagueis the Wise, a Sith Lord who learned to conquer death. It's a cruel twist of fate when we learn in Episode III: Revenge of the Sith that Darth Sidious was able to seduce young Anakin Skywalker to the Dark Side with the promise of cheating death. 'Wisdom they held, but that library contained nothing that the girl Rey does not already possess.' A-ha! It seems that Yoda's last words in The Last Jedi can in fact be taken quite literally. Of course, it seemed that the last remaining books of Jedi wisdom were burned as well, but eagle eyed viewers spotted those books on the Millennium Falcon, safely with Rey. The Last Jedi opened up even more Force Ghost possibilities, with Yoda calling down lightning to set the Force tree on fire on Ahch-to.
