A student of Tim Miller's once said at a workshop that I was attending that Tim had advised her to think of her practice in terms of decades rather than in days or months.
It's been more than 10 years now since my first led Ashtanga class. I've been hanging on for about 9 years of regular practice; it's been a mix of Mysore classes and home practice. The biggest shift in that time has been a move from focus on the physical to focus on the mental. I found the primary series exhausting and daunting for a long time. I don't now. It's comfortable, familiar and soothing to my nervous system. On the one day a week that I practice primary now, it's a joy to do.
It's interesting to me that although the poses that present my daily challenge in the intermediate sequence ask increasing physical efforts from my body, it's really the mental challenge in this sequence that I find the hardest. Kapotasana is an intense, deep stretch, but it's really the mental challenge of convincing myself to go there and then to stay there that I wrestle with. It's much the same with Karandavasana. That pose asks so much strength from my body. The biggest challenge for me is staying with it and using all the strength that I have to do what I can. It is so easy to let the mind convince me that "I can't" and then give up and fall out before I really have to.
A similar shift has mirrored practice on the mat in my life off the mat. I started practice with a lot of physical irritation. I wasn't crazy about the body I was given and would have gladly traded it in for a different model. I felt glued to body image issues lingering from childhood and teenage years.
...and while there are still ghosts of that "stuff" that I notice from time to time, I am physically generally comfortable now.
The big lesson of the first decade for me seems to be: "when the body goes mostly quiet, you can really hear the mind...and it is LOUD!"
The primary series has done it's work and for the most part left me with less "physical white noise". Now I watch the second series push all my buttons and listen to my mind yell in protest. I can't wait to see what the next 10 years will bring. :)