Well, I'm no master but....
We have 6 blackbelts attending our studio right now, of those 6, 4 are what I consider to have alot of natural talent. Coordination, flexibility, a good mind-body connection, and can internalize information rapidly. My instructor isn't one of those six and he laughs and says it took him 9 years to make black, and that he is largely responsible for his instructor not having much hair left. Having tried to teach him a new form that I brought in, well, lets just say I'm glad I'm not HIS instructor.

That being said, he is a VERY good fighter and a better instructor, it might have taken him a while to learn, but what he got he GOT.
I was a natural, I learned fast and could make things work pretty rapidly. But it hurt me, I would do it "right," but I didn't know why I was doing it that way. When I started instructing this deficiency showed up pretty quickly. It probably took me a year+ to figure out all the "whys" of what I was doing.
One of my fellow instructors was a brown belt with me and we tested for black within six months of each other. We studied together and I KNOW how much harder he had to work than I did to learn the material, in many ways I respect his black belt more than my own.
Lamont