How do the Elites in Halo become the Arbiter?

arbiters are the best soldiers(elites) in the entire race sent to do the most dangerous missions for the cause. Almost all arbiters die because of there job. That is the reason the new arbiter (halo 2&3) got the job when he was supposed to be excecuted(because the prophets hoped he would die on the job). So basically you just have to be a badass( i just made made this up but it sounds true so id just stick with it.