Causes do not put nature, Prakrti, into motion. They only remove the obstacles and coverings, like a farmer breaking down the barriers to let water flow in the field. The hindrances removed by the causes, Nature impenetrates by herself. (Commentary by Shri Brahmananda Sarasvati)
The first part of this yoga sutra states that incidental events do not directly cause what is bound to happen anyway. The second part of it uses the farmer (ksetrika) as an analogy. A farmer would remove the earth mound surrounding rice paddies to let the water flow through, in a way that nourishes the rice paddies and not merely flooding it excessively. The action of removing the earth mound did not cause the water to flow, it merely removed the obstacle at the right time.
When contemplating this yoga sutra, I thought of how my experience in becoming a Jivamukti yoga teacher is similar. I had a secure job that paid well at a reputable company at that time. Then, I was made redundant, and upon losing that job, I took my Jivamukti teacher training. I now understand that losing that job did not cause me to become a yoga teacher. I was already headed towards that direction. If that weren't the case, I could easily choose to take another similar job at a similar company. Losing that job was not an obstacle; the job itself was an obstacle removed for the natural path to happen.
When I think of it this way, I find the yoga sutra both empowering and reassuring at the same time. It is empowering in that it means our practice and intuition and wisdom will lead us to having the courage to remove obstacles when the time is right; reassuring in that events that are unexpected and may appear as unwanted in the beginning may simply be barriers being removed, and just requires our foresight to be able to see it.
It is of our nature to be happy and free, as it is the nature of water to flow freely. This yoga sutra asks us to examine where there may be barriers and obstacles, and how we can take action to open the doorway to what is already there. If we see the path as a naturally occurring one, it also means it will feel right though not necessarily easy. Once the blockages are broken down and the doorway is open, we begin to walk the path of least resistance.