My favorite translation of the Yoga Sutras of Patanjali is by Sri Swami Satchidananda. He gives a great description of sutra 6 of book II regarding where the ego lies in our yoga practice. He speaks about the difference between our true self and our ego self, describing these two as capital I and little i. He says that the ego self or little "i" looks an awful lot like our true self or capital "I" but is blemished by that single, simple dot...the one that always seems to undermine our authenticity.
In our yoga practice, I think the ego manifests itself in a few ways. First, we struggle with the challenge of truly listening to our bodies when entering the asana practice. We sometimes get caught up in a competitive state of mind and stop listening to our body's intuition. Second and conversely, sometimes the moment our teacher cues us into a pose that we find challenging, we give up or more truthfully give in to our ego's desire to only do the poses we know we can truly rock. Ultimately, both of these ego driven thought processes are an impediment to the unfolding of our practice and the discovery of our true self.
The next time you step into the yoga studio, place your ego right next to your shoes on the shelf in the lobby. Bring only what you need through the double doors...your mat, your breath, your intention and your capital "I".