The 3rd of the five niyama or commitments from Master Patanjali’s Yoga Sutras – to embrace spiritual hardships for higher goals.
If a physically challenging practice like sacrificing one's own sleep in order to be of service to others is done with wisdom and understanding, it can only bring a good result. Done sweetly and with joy, asuterities like circumambulating a holy place 100,000 times build a hardy constitution and physique. Feeding only your children organic food because you can't afford to eat it as well builds a strong immune system capable of resisting infection. It's the purity of the intention that brings the unexpected result.
Undertaking mentally difficult practices like assisting those in their endeavours of whom we are most jealous brings us every success imaginable. The mental discipline required to sustain a daily spiritual practice cultivates a serenity able to withstand the demons of doubt and fear.
Subtle Body Benefits
Pushing ourselves a little spiritually develops and strengthens our nadi system to support ever increasing volumes of pranic energy drawing into the central channel. This equates to ever increasing happiness and contentment.
Triumph over all obstacles to spiritual practice by exercising our ability to withstand, even flourish, in the face of calamity and turbulence, especially if we keep our cool when someone blows up at us or otherwise pushes our buttons hard! This is the highest and most difficult form of tapas. Most powerful if hardships are consciously used as a spiritual practice.
Much like the tapas "small plates" you would order in a Spanish restaurant, the Sanskrit word tapas suggests "spiritual heat" - in small doses, as our capacity allows! The Guru or Teacher generally metes out these spiritual austerities - mostly because our potential to take on hardships for the sake of spiritual progress can be an enitrely foreign or abhorrent idea! Left to our own devices, we are generally mired in tamas, rather than seeking out tapas! Tamas is another Sanskrit word that describes a phlegmatic and "stuck" state. Shiva himself performed the extraordinary spiritual austerity of knowingly drinking of poison so that his devotees could be cleansed of the poison of their tamas guna or tendency to indifference. Tamas is one of the three gunas (or qualities), the other two being rajas (passion and activity) and sattva (purity, goodness). Tamas is the template for inertia or resistance to action, whereas tapas is exemplified by powerful, even fiery action undertaken to hasten spiritual realizations. These can take the form of thoughts, words or actions which appear to us to be inherently "difficult or challenging" - to our current perception - and produce the effect of allowing us to move beyond this perception and progress spiritually.
Bhakti Yoga (devotion) and Hatha Yoga (physical practices) offset the potentially intense introspection of this practice.
If in doubt about whether or not to endure hardship, always check with your Teacher. Hardships such as standing on one leg for two years do not qualify as tapas!