In plain words
There is nothing called a beginning to karma. It is not possible for anyone to say what is going to happen, for what reason, when, or in what manner. This has been happening beginninglessly and continues to this day. Just as doing a piece of work is called karma, so too not doing any work at all and remaining idle is called karma. Seeing people who are sitting idle, we commonly say that they are not doing any work. But if we ask again what he is doing while doing nothing, the very same answer comes back -- that he is doing nothing and remains idle. What does 'remaining idle' mean? It becomes known that, by not doing anything and keeping still, he is performing the very karma called 'keeping still'. Therefore it must be understood that a man performs one karma at one time, and at another time performs the karma of not doing anything at all.
Karma and akarma, we must consider, are both karmas that are at once different and not different. One must see akarma within karma, and karma within akarma.
Inhalation and exhalation, the pulsation of prāṇa, is the very first act in life. That this keeps happening is a very astonishing, wondrous matter. No man resolves that he must breathe in and out and then does it -- this act happens without any volition. This is seen not in human life alone, but appears among all living creatures. A doubt may well arise in us as to how this happens without volition, and how no act at all can exist without volition. An act does not proceed without volition. So it is reasonable to say that the volition present in the act of breathing simply lies outside our field of vision. If, instead of accepting that, one tries to satisfy oneself that this is simply Prakṛti for all living creatures, then the question 'what is Prakṛti?'