In training Luke Skywalker, Yoda saw fit to expose him to the 'Cave of Evil' deep in the swamps of Dagobah. When Luke asked what he would find in the iconic Star Wars location, his Jedi master informed him, "Only what you take with you." However, this cave was also used by the Sith, who had a different perspective on its abilities.
Years after Luke's training, the cave was also used by Snoke to train Kylo Ren in Star Wars: Age of Resistance - Snoke #1, by Tom Taylor and Leonard Kirk. For the Sith, the Cave of Evil is meant to be a place they can use to purge the weakness from themselves by embracing their darkest thoughts. When Kylo asks what's inside, Snoke says, "Only what you've been too weak to bury." This is a fascinating accompaniment to Yoda's explanation, showing how the Jedi and Sith regard this experience differently.
The Sith & Jedi Both Harnessed Dagobah's Force Vergence
Dagobah is a Force vergence, where powerful energies naturally gather. In fact, the swamp planet is considered to be one of the purest Force locations in the known galaxy, with its sheer amount of energy helping to hide Yoda during his exile. Inside the cave, Luke saw and fought himself as Darth Vader, while Kylo Ren sees first his uncle Luke, then his parents. Kylo kills his uncle, but he is unable to kill his parents, proving not only his true fears but the emotional roadblocks that stand in his way to fully embracing the dark side.
Dagobah Reveals the Jedi & Sith's Different Uses for Fear
In many ways, the Jedi and Sith regarded fear in the same way - as the path to the dark side. However, while Jedi saw this as a tragedy, the Sith viewed it as a way to gain immense power. It therefore makes sense that while they are each confronted with their nightmares in the Dagobah cave, Luke and Kylo Ren react in opposite ways. Luke slays "Vader" but gains insight into his fear of the villain and his own potential for corruption, ultimately rejecting the Sith way and redeeming his father. In contrast, Kylo Ren can't bring himself to harm his parents in the cave, but this only makes him see doing so as a limitation he must overcome, and he later kills his father in response. To the Jedi, the cave shows them the fears they must process to stay with the light, but for the Sith, the cave summons the nightmares they need to embrace to enhance their power.
Dagobah is an incredibly Force-sensitive planet and because of that the Force vergence known as the Cave of Evil has been used by both Jedi and Sith as a training ground to identify fears. However, each group's perspective on that experience is totally different, and while the cave gave Luke Skywalker valuable insight into his own potential for darkness, the Sith philosophy of Palpatine (via his clone puppet Snoke) persuaded Kylo Ren that he could only conquer his greatest fears by making sure they came to pass.