bjj has a pretty high learning curve in my opinion. It is similar to wrestling/judo/boxing/muay thai in that way. And because of this, many people quit when it gets tough or they plateau.
Personally, I was the very worst one of the bunch when I began bjj in 2004 at college. Although compared to the world class competitors of today, I feel insignificant, I also feel that I made huge improvements and learned quite a lot about my own capabilities.
I've heard the saying "A black belt is simply a white belt that never quit", and definitely feel that there is some truth to that.
Above all attributes (athleticism, speed, strength, etc.), I would value the determination to train consistently above it all. Just my 2 cents.
Now here is an amazing no gi match between Wilson Reis and Justin Rader