At this time, it would be wise to remind us that nirjara is done most effectively by humans only, because other destinies have their own limitations. But for humans, the limitations are set by humans only. The special efforts to destroy karma is done through Tapas or austerities. Austerity means restraint, which is done willingly by giving away some of the bodily comforts to discipline our mind from passions and pleasures. Austerities are performed at various occasions and in various different ways.
All austerities have their own uniqueness.
In the physical manner the person performs the austerity, but does not have the inner desires to change his or her life and therefore, it is just a physical act. While in the psychic austerity the person controls his or her inner desires along with performing a physical act. Unless the austerities are performed in psychic manner, they do not produce the much needed results. After all, the whole purpose of austerities is not just to simply make the body suffer, but to change our desires. Once that happens the person will be on the path to spiritual uplift.