In Star Wars, the Sith have a Rule of Two which states that there must be two siths, no more, no less. Basically, it's flexible because it's survival of the strongest so they have to try and kill each other and make themselves stronger and stronger as the generations go on. Simple, right? Well, in the Destiny lore, there is quite a similar rule, the Sword Logic. That is also 'survival of the strongest' with swords, so like lightsabers, AND THEY ARE USED BY THE DARKNESS, THERE ARE TWO HIVE LORDS LIKE TWO SITHS, AND THE DARKNESS IS LIKE THE DARK SIDE BECAUSE THEY USE THE DARK SIDE OF THE FORCE. *sigh* I'm ashamed....