Oh, you’re so flexible.
Yes, after more than a decade of practicing Ashtanga yoga I got flexible.
A stiff person can become flexible. It’s possible.
On the picture is not a flexible person by nature, but someone with discipline. The form is only the surface.
I didn’t give up and worked on my crazy goals to lift my legs in that pose. If you try this on a daily basis for years, frustration is inevitable. But one can stand this feeling of frustration. It’s temporarily.
Something went wrong, I thought. I explored the pose and found out that it makes no sense trying to lift up the legs. I pointed the feet and stretched the legs forward. Suddenly the heels were away from the ground. They lifted from alone. Reaching the goal was more or less a side effect.
One could formulate a philosophy from this experience: Stretch and you’ll lift.
Or: Do something differently.
Or: A decade is nothing, keep practicing.
An asana has reached a peak level, when the outer form is correct AND when the asana feels good. Right now kurmasana is possible, but it doesn’t feel good. To hold the pose for 5 quick breaths is enough. There is room to develop this pose again. One day it will be pure pleasure again to stretch into this pose and to relax.