I dont think that everyone who practices jiu jitsu can achieve a black belt. I think it is a combination of knowledge, application of that knowledge, physical ability, intelligence and mental toughness that enables someone to achieve it. That being said, you dont have to be a great teacher or a great competitor to pull off this huge accomplishment. As matt said, you should have the ability to help the lower belts if they need it, but some people just dont have it in them to be a teacher. Its a lot to ask, youre asking students to have complete faith in you and trust that what youre teaching them is right. That is a lot of pressure for some people. On the other side of the coin, some of the best people i have had the pleasure of training with never compete, for them its not what jiu jitsu is about. My instructor recently awarded his first black belt to a fellow student, and while he has only competed a few times in his 11 year jiu jitsu career, he is an amazing jiu jitsu practitioner, one of the best i have ever rolled with. He is actually a great teacher as well, but we also have a ten stripe brown belt at our school who whoops some serious ass at competitions, but for some reason he has some difficulty when it comes to putting technique into words that lower ranked students can comprehend. So I personally believe you can earn a black belt while not being a great competitor or a great teacher, but thats just one mans opinion. What do you guys think?