Why do the Sith Masters encourage their students to try and kill them if they become weak? I never got this. If you're really evil, the first thing you do is change the damn rules so that the apprentice doesn't kill off the master. I mean, they'll probably turn on you eventually, but do you really want to encourage that sort of behavior? "Go ahead. Kill me. I want you to try!" If you're amoral, you shouldn't really have any problems changing the system so it benefits you and screws your underlings. Just raise the little tyke from infancy to be a mindlessly loyal dark side slave that won't hesitate to sacrifice themselves at your whim.