Everyone will find, at some point in their yoga practice, that there’s something they “just can’t do”.
That’s how it feels, anyway. But stop and ask yourself what you’re really saying. You can go on the internet and find all sorts of images of people of all sizes, shapes and ages doing any yoga pose you can think of. For most people, there’s no reason why you, and you alone, can’t find a way to do this pose – whether it’s through modification, practice or using props. The best thing to do is ask a yoga teacher how to modify a pose to allow you to really practice it. The second best thing you can do is to ask other people who practice yoga what they do to make the poses easier.
The worst thing to do is to tell yourself you can’t do it. That’s not true. You just can’t do it now.