One who is intent on practice will obtain Siddhi, not one who is idle. Yoga-Siddhi is not
obtained by a mere reading of the scriptures (Shastra's). Siddhi is not achieved by wearing the dress [of a Yogin], or by talking about it; practice
alone is the cause of success. This is the truth, without doubt.
Hatha Yoga Pradipika I. 65-66
(translation by Srinivasa Iyangar/Tookaram Tatya)