“The Yoga Sūtra of Patañjali deals with the mind.
It examines the different functions of the mind
and provides means to modify these functions
so that it serves the person in a very constructive way.
The means by which certain qualitative changes in the mind
are brought about is called Sādhanā.”
– TKV Desikachar on Śraddhā in the Yoga Sūtra