So after recently rewatching season 4, all the mention of 'the rules' got me thinking, maybe one of the rules is that the island's leader can't kill his predecessor? That may explain why the Nemesis said 'Do you know how badly I want to kill you right now?', maybe if Jacob was the first leader, then the Nemesis, then Widmore, Ben and finally Locke. So the Nemesis couldn't kill Jacob, Ben could'nt kill Charles, and maybe that's why when Jack (The Losties original sole leader) tried to shoot Locke it didn't work? But Ben could kill Jacob because there was another leader between them? Like if you placed them in a line, Nemesis, Jacob, Charles, Ben, Jack, Locke. Nemesis could kill anyone in the line, apart from the Jacob. Or maybe it's just that leaders can't kill leaders? Otherwise everytime someone tried to overrule the leader they could just kill him, which would also explain why Widmore got Keamy to kill Alex? Because that would make Ben want to step down as leader, to go to the mainland and go after Charles, but maybe even though neither of them were the leader anymore they still couldn't kill each other, which is why Ben went after Penny? Sorry if you can't understand this.