Yoda's words proved true in the old Expanded Universe, with Luke manipulated by the resurrected Emperor Palpatine into briefly embracing the dark side in the Dark Empire comic book adventure. Years later, Luke came to realize his brush with the dark side had tainted his use of the Force, leading him to focus on using the Force for power rather than wisdom and insight. Those stories were branded "Legends," that is to say non-canon, when Disney acquired Lucasfilm in 2012; but, curiously enough, the same pattern is playing out in the new Disney canon as well.
which Force power Luke was using when he began exploring Grogu's memories, but it seems remarkably similar to the Mind Probe - a related power to the famous Jedi Mind Trick, but one that is associated with the dark side and appears to have been taught to Sith apprentices early in their training. Novels set during the High Republic Era, some 200 years before the prequel trilogy, have revealed the Jedi traditionally viewed any mental power as a little too close to the dark side for their liking, because a Jedi who used these techniques would face the temptation to abuse them and violate another person's mind. It's actually quite disturbing to see Luke Skywalker using this power even as he has droids construct his new Jedi Temple.
Sadly, Luke used the Force to peer into Ben's mind while he was asleep; not only did this betray the bond he shared with his apprentice, it was also an act of violation that is most certainly dark in nature. Little wonder Palpatine was able to twist this to his own end; the Emperor's Force presence had been with Ben for years, manipulating him, and it's even possible it was the Emperor's own darkness Luke really sensed. Palpatine's voice awoke Ben from his sleep, and soon Luke and Ben were locked in a desperate duel. With Luke defeated, the Emperor lashed out with the Force, destroying his entire Jedi Temple.
It's tragic to consider that, even in the Disney canon, Yoda's words were right. Luke Skywalker started down a dark path, and it did indeed forever dominate his destiny. The Luke Skywalker of The Mandalorian season 2 and The Book of Boba Fett may be clearly seen as a hero, but already his flaws are there, and the Force power he used on Grogu foreshadows the mistake he would ultimately make with Ben Solo - one that would almost wipe out the Jedi when Palpatine destroyed the Jedi Temple. Star Wars has turned the story of Luke Skywalker into one of tragedy, as the celebrated Jedi Master failed to recognize his own weakness.
