system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] If the Sith were so selfish and evil, why would they bother with the rule of two? Why set yourself up to be killed? I get that it's all to make a more powerful Sith in the long run but that doesn't seem selfish, it seems nice and selfless.

Is it so you can have your power until you die and then pass the dark side torch to another person, cause that's what I think. Still, why would Palpatine not stay on his own and just live forever or whatever? He doesn't have to share and why would he help some future asshole get more power, that's not the Sith way.
gpt
Much easier to control one pawn, than having hundreds of other competing Sith lords, who are constantly backstabbing each other. History proves Sith end up doing this, again and again. Sith lords are painfully aware of it.

Having an apprenice is practical. They are a tool who does the shitjobs while you can carry on scheming.  
Like you say, it is a matter of holding back information, and making sure the apprenice needs you at least as much as you need the apprenice.  

All sith are full of themselves. It is in their very nature. All of them believe they will be the one to break the cycle, and stay Master forever.