The reason I say that my rank exceeds my abilities is that I think the blue belt was more of a parting gift from my sensei than a true measure of my skills. But at the same time I respect him and his judgement, I have only been training BJJ for 1 year after 5 years absence from Judo.
Michael - you'll know if you're worth a BJJ Blue belt if the people that walk in the door don't offer much of a challenge any more.(Unless that person is a 140 kg muscle bound monster). That's my simple theory.