I agree - don't be afraid. I have had this one since the intensity series came out. I can't tell you how long it took me to master it because I'm still working on it! I just do what I can, and modify a lot. I still, for the life of me, can not do interval 3 - I just skip it (don't tell the workout police).
Right now, I have mastered Interval 1, 2, 4, 5 and 10 but remember, I have had this workout since the series came out - must be well over a year - right? I'm working on learning the other intervals.
Sometimes I'll be doing it and like magic, I can do a move that I couldn't before - it just takes practice - I still have problems with any figure eight turning move and over the top backwards moves - when she is doing that, I just sub in something I can do with high intensity - like knee ups corner to corner or some other move that I can do.