Because there are so few belts in BJJ you often find that you can tell someones belt level simply by rolling with them. That line really starts to blur at brown and black belt. I found it really hard to distinguish what black belts did when I was a purple belt. It became less about technique and more about decision making/thought process. As a brown belt I find that I still don't have a very set "game" or style. I use no guards save perhaps butterfly and I have like 3 guard passes. The panic sort of started when I realised I'm a few years off my black belt and starting my own gym and I'm not at the same level as my instructor. There are still basic things I can't do right and would feel awkward teaching because of it. Some things I've practiced for years and still struggle with the feel of it. d'arce chokes and reverse triangles. I'll catch inexperienced folk but if someone knows how long they can hold out before a tap I often won't get it. So now I'm left wondering what the difference between a black belt and a brown belt even is? It's so hard to distinguish.