It is only when correct practice is followed for a long time, without interruption and with a quality of positive attitude and eagerness, that it can succeed.
There will always be a tendency to start practice with enthusiasm and energy, and a desire for sudden results. But the continuing pressures of everyday life and the enormous resistance of the mind encourages us to succumb to human weaknesses. All this is understandable, we all have these tendencies. This sūtra emphasizes the need to approach practice soberly with a positive, self-disciplined attitude and with a long term view toward eventual success. This is how TKV Desikachar explains this sūtra in Heart of Yoga. I liked the explanation a lot.
Practicing something with enthusiasm and eagerness is the key here. One should look forward to the practice. I think I can use Sachin Tendulkar to explain this. I don’t mean to scare a novice that tries this path of yoga by using Sachin.
Sachin Tendulkar never tires of the game. Twenty years in international cricket and he retains the enthusiasm of a schoolboy. He spends time with the younger boys at the nets, bats with great intensity and comes out of the session smiling. It’s remarkable how this man continues to enjoy his cricket.
This again is not easy advice. Many people start a task with so much enthusiasm and then they fall off. To keep it going and get over the hurdles of the mind takes someone that sees meaning in doing this. One cannot fake it as a true passion is a must to do something like this.
I remember reading something related to this concept in Yoga Makaranda by Sri Krishnamacharya. I found this book at Sri Ramana Maharshi ashram library in Tiruvannamalai. He says that taking the spiritual path is not some business that you do in a market. You put in month’s effort of time and expect the results worth for a month. You must wake up at 4 am and go to the river, take a bath and prepare for the practice. You do it for at least two hours and then you keep doing this for at least a year. Then maybe, you can see some changes. This is something you continue all your life. I liked this small book as it was written when Sri K was still an angry man. He was such a perfectionist, you can feel it in his writing. He is said to have sobered in the later years of his life.
sa tu dīrgha kāla nairantarya satkarāsevito dṛdha bhūmiḥ
sa – it, here, this
tu – but
dīrgha – long
kāla – time, from root word kāl which is to impel
nairantarya – continuance, here: uninterruptedly, from root word nair + anta ‘between’ + ya, lit. non-between-ness
sat-karā – right fashion, here: properly from sat ‘right’ + kr is ‘to do’
āsevito – cultivated from ā + sev is ‘to resort to’
dṛdha – firm, firmly from dṛmh is ‘to fasten’
bhūmi – earth, here: grounded from root word bhū ‘to become’

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anta is not antara.
nair+antar+ya
May be you are right. I see that the ‘r’ is missing.