5. Japanese Society
The martial arts -- in particular, Japanese martial arts -- grew out of a very hierarchical social structure. If you started learning with a group of peers, it's important that you "keep pace" with your peers in terms of grading, otherwise you can create awkward situations when former kohai become your sempai. Now, you can mitigate some of these awkward topsey turvey situations with grace and humility, but it's easier if the peer groups advance relatively together.
As you progress in grade, your responsibilities increase in the dojo. Avoiding gradings is in some ways shirking this responsibility. (The kind of thinking that goes: "Oh, I'm not interested in grading. I just want to practice," is ultimately, in this context, a very selfish approach.) A corollary to this is that as you progress in grade, you start to take on more teaching responsibilities -- and when you teach, you begin to understand things about your own practice that you hadn't thought about before. And the higher the rank of the student you have to teach, the deeper you have to go into your own practice.The other day, Michael gave me another one, which was mirrored in a comment by Mr. Watson (from England).:
7. Milestone indicator
Since a martial artist is always training to continuously be better, a static rank has very little meaning. The individual's performance of Iaido one day can be vastly different than the next. A first year 5 Dan Iaidoka will be vastly inferior to one that is about to challenge their 6 Dan exam. So what does the rank tell you about an individual? Right now, nothing. Look over the lifetime of one's training and it starts to have some meaning.
Where you have been? What have you learned? The specific criteria at each Dan level provides a glimpse of what should be focused on in a predefined arc of progression. The seniors that came before us discussed long and hard on these indicators of performance and understanding, so that we may achieve our potential that only the highest levels can perceive, and hopefully for us to surpass.
To ignore these indicators is to hinder our own progress in the arts.