For someone who decried the idea of suffering for the sake of others, Darth Bane's entire evil scheme rested on the willingness on the part of generations of selfish psychopaths to matyr themselves for his philosophic ideals. All it would take for his entire grand plan to fall to pieces is one, just one, Sith Lord to decide, "You know what? Screw the Sith Order! I'm in this for #1." and then act on it. Rather than risking their necks for the sake of the approval of some dead guy, this hypothetical Sith Lord would simply not take an apprentice at all, merely using their powers for personal gain as they saw fit. Or, if they wanted/needed an apprentice, simply deliberately selecting one with a much weaker connection to the Force, followed by a deliberate crippling of their training. Voila! A Sith apprentice powerful enough to be a viable lackey, but far too weak to ever hope to overthrow their master. Rule of Two, broken. So why exactly was Bane so confident that a bunch of lunatic sociopathic egomaniacs wouldn't simply decide they don't give a damn about him or his rule and ditch the whole thing?