I guess my issue is that when I see people doing things I can't do, even with trying, it gets me mad. Reminds me of my "weaknesses." I'm the same way with cycling, running, and x country skiing. I know my limits, I've pushed past quite a few of them, but some things I just can't do. I may want to do them, but I either haven't practiced enough, I'm too scared, or I give up. Since this is such a "non-yoga" attitude, I found that when I was going to classes at my gym (which were taught by very good instructors), I learned who did things that I was at least OK with and I also never went to anything too advanced, usually mixed level 1 and 2, sometimes level 2, never 3. Come to think of it, I am also happier riding with people who are slower than me. Don't like to be reminded of what is hard for me. I think deep down I am very competitive, despite the fact that I was brought up in a very non-competitive home. It's just too bad I didn't harness some of this competitiveness into athletics when I was younger.
Totally not what a yoga class should be about, but, honestly, the way I feel.