Yōga Sūtra 1.01

अथ योगानुशासनम्।

Now the self-discipline of yoga (is explained).

All sutras or aphorisms in Samskruta language are short, cryptic memory aids to be taught by a Guru to his/her disciple in close physical proximity with oral explanations and practice. Due to passage of time, much of the knowledge is lost and what remains is only aphorisms. Hence many times we are constrained and left with no choice but to extrapolate some of the implied meaning from the available knowledge sources.