As promised, more eloquent words from Mr. B.K.S. Iyengar:
"If you want a simple way to remember the relationship between asana and concentration (dharana), it is this: If you learn a lot of little things, one day you may end up knowing a big thing."
from his book 'Light on Life'
In the Ashtanga tradition, asana is only one limb of the 8-limbed practice. Ashtanga literally means "8-limbed". Concentration (dharana) is another limb of the practice. Yet, the way in which we practice asana is also the practice of dharana, concentration. We bring our attention to what we are doing right now. When we notice that our attention has wandered (maybe when we wobble out of a pose :) , then we bring our attention back.
I love the suggestion in Mr. Iyengar's choice of words, that this work takes time! Concentration is not easy, but I know everything else is easier for me when I put in the work on concentration. As Mr. Iyengar puts it, I hope that one day I too "may end up knowing a big thing"!