I had a conversation one day about aiki and aptitude where I stated I thought a lot of the success someone could have with learning aiki depended upon their natural aptitude to understand and learn the particulars required. The person I was talking to thought that it was more a matter of attitude or perseverance and work that made a major difference. IMO, all are important, but if you have two people putting in the same level of effort in training, it will be the one with the better aptitude that will excel over the other. Now if you take someone with great aptitude AND extreme attitude coupled with extreme perseverance, you just might end up with an O Sensei or a Sagawa
I think natural aptitude can only account for a miniscule amount of progress compared to perseverance. Some of the people I've met that think they have a natural aptitude to understand aiki, do'nt seem to have the perseverance to do the work to really get there. But then, I might think that as I'm one of those lacking the natural aptitude.