In the real world, the Dual Rule came about because George Lucas decided that a master and an apprentice had the Emperor/Vader structure ingrained in Sith culture for centuries. According to the retired filmmaker, the Sith ruled the galaxy at one point, but their greed and selfishness led them to infighting and killing each other.
Things just kept going like this There’s a Sith left named Darth Bane. Bane then took an apprentice, after which the apprentice would kill the master when they were strong enough and take another apprentice who would eventually replace the new master. We see this in movies that Sidious is hiding. to replace his dying apprentices, from Maul to Dooku and then to Anakin. Anakin’s goal is to kill Palpatine and have Luke as his apprentice until the Jedi saves his father and breaks the cycle.
Although Bane is mentioned in the novelization of “The Phantom Menace,” his story wasn’t properly told in a trilogy until 2006 by Drew Karpyshyn. Bane destroyed the Sith Order to create a new one and established the Dual Government, which would ensure that there were no more than two Sith at a time, resulting in the growth of the Sith by transferring power from master to more powerful apprentice. stronger with each cycle.
But things changed when Darth Plagueis decided to defy the doctrine and later tried to unravel the secret of immortality with his apprentice, Darth Sidious, who betrayed and killed his master and tried to finish his master’s experiments with immortality. During “The Rise of Skywalker”, Sidious somehow succeeded. As of now, Palpatine technically broke the rule before he definitively died in the canon.