The Yoga Sutrasare a book of condensed instructions. Like many ancient & historical texts, they require background knowledge and contemplation to fill in the weave around the threads and in fact one translation for “sutra” is thread. The Sutras are threads our minds may weave with meaning and our bodies may find support when we follow.
One of the few sutras which instructs us on the physical practice of yoga is II.46: “Sthira Sukham Asanam.” "Yoga pose is a steady & comfortable position," according to Mukunda Stiles’ translation, which is highly recommended by this author.
Clearly, if you’ve been to any yoga class, this doesn’t mean we don’t challenge ourselves. In fact, in T.K.V. Desikachar’s more recent book The Heart of Yoga: Developing a Personal Practice, he writes, “A further meaning of the word yoga is “to attain what was previously unattainable.” … when we find the means for bringing that desire into action , that step is yoga. In fact, every change is yoga. For example, when we find a way to bend the body forward and touch our toes, … Each of these movements and changes is yoga.” (p. 5-6)
As yogis, we choose to cultivate our awareness in a place of kind, curious observation while going into places and experiences and thoughts we were not aware of before. Our body is our first, most personal playground for this. So if the challenge today is a forward bend, in yoga our measure for success is not how forward the bend is, but how aware we are in the effort. Are we able to maintain equanimity in effort, to remain steady and make adjustments so our basic stability & comfort are not lost? Yoga is about cultivating curiosity with kindness and understanding what is rather than fixate on what we think we wish would be. Our concern with knees and toes and bellies and heads and backs is one of care and curiosity, and because of that - joy.