Yogasūtra I.32 - tat-pratiṣedha-artham-eka-tattva-abhyāsaḥ

If one can select an appropriate means to steady the mind and practice that means, whatever the provocations, the obstacles cannot take root.

Committing to a “singular principle” is a long-term commitment to a chosen path. Rather than spread our energy in different directions, Patañjali is suggesting that we divert all our focus into one appropriate set of practices.