The other day, one of my yoga peeps mentioned that she was worried about "losing" one of the poses she recently mastered. While I am no expert by any means, in my experience, I have found that sometimes poses come easily and sometimes they don't. One day you can have the best practice ever and the next you find yourself struggling to get through.
Like anything in life, I feel like yoga practice ebbs and flows. A pose may take 5, 10 years to master and once you get it, you get it, but your body can betray you and you can lose it too. And it's ok. I have found the less I talk about how well or poorly I do a pose and the more I actually practice doing it (properly, of course!), the better it gets. I also have found that as soon as I feel like I am "advancing" in my practice, something happens to pull me back.
My left wrist has been hurting over the last month. I have had a hard time bearing my full weight on it doing upward facing dog and have been modifying some poses to alleviate any pain. I've mentioned it twice to my teacher so he knows I am not cheating, but otherwise I don't like to complain. I am slowly bearing more weight on it so I am keeping my fingers crossed my condition is improving.
My best advice to my friend is to not worry about that certain pose too much and just keep practicing. Your body will let you do it when it's ready. Namaste.