With the popularity of yoga growing & that many people doing yoga, it is natural that not everyone can accomplish everything they are asked to do.  Looking around whether on websites, in magazines or seeing others on their mats, you might see that some people are really open, strong and flexible.  Really it is all in how you look at it.  You can take great inspiration from those people or it is also a little bit possible to get a bit bummed out about it because you can't do what "everyone else" can do.  Having said that, there is a great mental antidote.  All you have to do is focus on how lucky you are to be able to do whatever it is you can do.  There are a great many people in the world that can not do a single chatarunga push up, or do Warrior 1 even it they wanted to.  In that respect  we are incredibly lucky to be able to practice today. So if this feeling arises in your mind, just focus on what you can do in your practice today.  Thru your practice and poses you may start to feel a sense of accomplishment for what you can do.
Much Love,
Taryn