What makes you think people do jiu-jitsu for fun?
People who do jiu-jitsu (and other martial arts) will tell you that "fun" is a wholly inadequate word to describe the experience. I never said it was about fun. It's about something much greater than simply fun.
I wear it because I want to be better, to improve
If you want to be better, to improve, at a martial art, metrics (and especially a wristwatch!) is the wrong way to go about it.
Kind of like a coloured belt.
If you want to be better, to improve, a "coloured belt" is the wrong way to go about it. If you study jiu-jitsu from those Brazillian guys, you think they're giving out coloured belts? You ask them for a coloured belt and they will throw you the fuck out. By all means go to Wudang mountain and study with the Shaolin monks (I have) and ask them when you get your "coloured belt". Let me know what they say.