I found this one on an Irish forum and thought I'd post it over here. Makes good reading IMO.
"One of my athleticley gifted newer blue-belts was asking me the other night "what is the difference between a brown and a black belt, is it just time? and what about those really good brown belts? who beat black belts?"
I first asked him to remember when he was a brand new white belt. Can you remember rolling with a solid purple belt, how it didn't feel any different from a brown or black belt? You could feel the technical difference between a blue belt and white, but not really the other belts. When you are a blue-belt, the "eager belt" you can feel the difference between purple-belts from brown and black, but brown and black still feel much the same. When you get to puple belt, thats when you see the technical differance between the brown and black-belts. Timing is refined, there is less reliance on attributes that you could'nt feel as a blue belt. Purple belt tends to be the "cockey belt" On a good day your hanging well with browns and blacks, But if you elimated attributes you would check-mated most of the time, although you you know exactly how it is being done to you. Brown belt is the "confident belt" your slowing your game down and refining the signatures of your game. Your much more able to detach from what "your doing" thus allowing you to really read your opponent. Black-belt is the "mature belt" your watching the "roll" almost from outside of your body, you clearly see and feel the differance between technique and attributes in both yourself and those you roll with. You observe the roll while your rolling.
To use the swimming analogy.........Brand new white-belts can't swim, they panic and lack techniques to survive in water, they dog paddle to exhaustion. Then they learn the basic strokes, they still relie heavily upon muscle based rapid, jerky body movement to keep afloat. Mentally they still panic. The new blue-belt has become comfortable in the water, he knows the strokes and can swim, although there is still that fear of drowning going on mentally. Movements are often forced. Purple is when you become extremely comfortable in the water "