There is also a green belt in my class who is really good. Part of this, I'm sure is do to his extensive experience in TKD and other arts. We were in Randori and he tried using one of my favorite counters, Tani Otoshi, but he couldn't quite land it. He asked me to allow him to practice it on me, and he had the gist of it, but it wasn't quite working. So I decided to demonstrate it to him. Boom - he came down with an ippon-worthy slap.
I guess that being a brown belt means knowing enough to be competitive, but nowhere near enough to be considered an expert.