Fightclub discipleship
I was chatting with Rob, Mark's housemate (and my ex-kickboxing teacher) last night. He's about to take his blackbelt and I was asking him about the dan system. Apparently what happens is that once you are a black belt, if you train someone else to that standard then you will be a first dan. If that person goes on to train someone else to the level of blackbelt then you become a second dan. It works in generations.

I'm sure there's a connection somewhere there with discipleship...