The japanese have a phrase, shoshin, which means "beginner's mind". The line above is from the Book "Zen Mind, Beginner's Mind" by Shunryu Suzuki, which presents the basics of the practice of Zen, from the details of posture and breathing in zazen to the perception of non-duality. Yet in my mind, Suzuki's opening mantra has as much to do with the practice of ashtanga as it does to the practice of Zen.
Suzuki says 'I am interested in helping you keep your practice from becoming impure." I love this.
For a while you will keep the beginner's mind, the excitement of getting on the mat, going through the familiar postures, being given new postures, but if you continue to practice one, two, three years or more, it is likely that you may lose the 'limitless meaning of original mind'.
Suzuki states that our original mind includes everything within itself, it is always rich and sufficient within itself, it does not need external 'stuff' to complete it. "You should not lose your sufficient state of mind". However, the mind's "richness and sufficiency" does not meant that it is full by any means, in fact the "original mind" is empty, open and always ready for anything.
I love the story of Aldous Huxley, who got to the point where he was so high all of the time, he got his vocabulary dow to just one word "extraordinary!", everything was "extraordinary", everything was blowing his mind all the time! That sense of awe is with everything that faces you on a day to day basis, you should look upon with the eyes of a child almost, with a fresh view, no pre-conceptions, language drops away, so there is just you and the experience.
"Self centred thoughts limit our vast mind". When we have no thought of achievement on the mat, when we just get on it and do the practice, accepting the way our bodies and minds are behaving at that given moment, we have no thought of self, we are true beginners. Then, Suzuki says, we can really learn something.
"When our mind is compassionate, it is boundless....then we are always true to ourselves, in sympathy with other beings and can actually practice."
There is no need to have a deep understanding of Zen to practice Zen, or a deep understanding of Ashtanga to practice Ashtanga. Never say you know what the practice is, because as soon as you do, something will change which will make you question the practice again. This is the practice of Zen, of Ashtanga, always be a beginner.