What does it mean to excel, to do well?  I think there is no excelling in yoga, at least not the way we conventionally think of excelling in school or career or sports.  But to practice in a way that is more than casual, there must be ardor–tapas. 

Tapas is often translated as fire, and the texts are full of stories of outrageous physical exertions done to prove the tapas of the practitioners looking for boons from the gods.

There is a fiery aspect to tapas, but I question whether it must necessarily be burning from physical exertion, though that is a path that calls out to many. 

The fire of tapas could be thought of as doing what it takes to manifest the will to know something deeply enough to be able to experience the fluency and grace and delight of expertise.   It could be the ardor to show up in a disciplined and committed way for hours and days and years of practice, always still wanting deeper, fuller knowing.