I will be the first to admit that it looks cool to get your foot behind your head or balance on your hands with your feet flying up behind you. I admire the shapes that flexible and strong students can make on their mats. But there is a limit to my marveling.
I will always try out postures and take my time with the preparation but most of the time, my foot is not going to get back there (unless something breaks or rips). Some poses are just out of reach for me now no matter how much I try, or train, or strain, or meditate on it.
Does this make me a failure?
Should I turn in my Yoga teacher card?
Do I need to go on some kind of fast to shrink myself down to some tiny size that looks like it will facilitate my getting that pose to look "right"?
Should I let a teacher force me into the pose either through their words or by their hands?
NO to all of that.
The manifestation of the practice of Yoga is not about the final position of our feet or the look of our final pose. The positions of our feet and these postures help us to attain higher levels of Yoga not because of the shape we achieve but how we journey to get there.
The journey to get into poses helps to open up lines in the body--energy pathways. The opening and clearing of these lines helps Prana flow. What is Prana? "Prana is energy, vitality, power. Prana is the foundation and essence of all life; the energy and vitality that permeates the entire Universe. Prana flows in everything that exists. Furthermore, Prana is the connecting link between the material world, consciousness and mind." So when we work to clear up the lines that help this energy flow can you imagine the benefits! So what if you are not able to tie yourself into a knot or get your palms flat on the floor in a forward fold with straight legs. The simple act of working on that fold had enormous benefit.
Therefore, enjoy your practice more. Strain and struggle less. Achieve what you can and let the rest just rest. Connect to Prana and start doing some deep Yoga.