Luke Skywalker's Jedi Training Set up the Dark Side’s Secret Origin

screenrant.com:

While the dark side of the Force is often presented as a natural part of existence, Star Wars Legends totally undercut this idea by giving a location from Luke Skywalker's Jedi training a shocking origin. In a famously ominous scene in The Empire Strikes Back, Yoda takes Luke Skywalker to a dark side-infused cave during his Jedi training on Dagobah, deeming it a “domain of evil.” However, a follow-up story confirmed the dark side presence in the cave isn’t naturally-occurring, and the story of how it began explores the difference between the natural Force and its corrupting dark side.

The Force and its dark side are a key component of the Star Wars franchise, yet the films, their ancillary material, and even their creators and fans don’t always agree on how they’re defined. The original trilogy, the prequel trilogy, and much of the now-defunct Legends continuity’s material treat the Force as an energy field created and nourished by the natural cycle of life and death, while the dark side is a seductive, addictive, and ultimately corrosive corruption of this natural energy, promising everything to its victims but leaving them with nothing. In the Star Wars sequel trilogy and ancillary material from the ongoing post-2014 canon timeline, the natural Force is designated the “light side” (something that was only a nickname for the Force in the previous continuity), with both the light and dark aspects of the Force being natural components.

Related: Darth Vader's First Apprentice Has the Dark Side's Most Horrific Power

'Heart of Darkness,' a story by Paul Lee and Brian Horton in issue 16 of Star Wars Tales, simultaneously demonstrates the original definition of the dark side of the Force and its characteristics while providing