Hey dj, I feel your frustration, but being out of your comfort zone, or "playing what you can't" is making you a better guitarist!

I'm not an expert and not a newbie, maybe a late beginner or early intermediate. Per moosehockey's advice, keep after it and know that it's ok to move on. What's easy for one guitarist is challenging for another, so think of it as an opportunity to identify your strengths and weaknesses. (But try to make time every practice session to address those weaknesses once identified!)

Get yourself to a good place where you understand and can command most of the lesson. Perfection is not the goal. Also, don't fret about "forgetting" other lessons. As Anders Mouridsen regularly points out in his Acoustic tutorials, learning, forgetting, and re-learning is a natural part of the guitar journey.

FWIW, last night I revisited some of Lisa McCormick's fingerstyle lessons that had been giving me fits a few months ago. They seemed to be solidly under my fingers when I tried again. But like moosehocky, Anders has me stumped on several of the practice tunes in Acoustic 1. I believe that with time I will revist these as well and wonder what all the fuss was about. Keep at it and you will be glad you did!

Just out of curiosity, where is the lesson in question on the website?