मूढग्राहेणात्मनो यत्पीडया क्रियते तपः ।
परस्योत्सादनार्थं वा तत्तामसमुदाहृतम् ॥ १७.१९ ॥

mūḍha-grāheṇātmano yat-pīḍayā kriyate tapaḥ |
parasyotsādanārthaṁ vā tat-tāmasam-udāhṛtam || 17.19 ||

In the tāmasika kind, it is ignorance and delusion that works throughout. The austerity that results from such delusion will naturally lose its very purpose. It will also be a torture to the mind, senses and body. To hurt or harm another can also be the objective. Any such wrong note or objective makes one’s performance impure and harmful.

Why is Krishna describing this tāmasika kind? There is enough scope for this note of vitiated performance to creep in, when we take the common human mind into account. One has to be careful against such vitiated notion, putrefaction at all times. Constant vigil and self-examination will alone help the seeker against such downfall.