Bhagavad Gita · Chapter 18: Freedom through Renunciation
Bhagavad Gita 18.35
यया स्वप्नं भयं शोकं विषादं मदमेव च ।
न विमुञ्चति दुर्मेधा धृतिः सा पार्थ तामसी ॥
yayā svapnaṃ bhayaṃ śokaṃ viṣādaṃ madameva ca | na vimuñcati durmedhā dhṛtiḥ sā pārtha tāmasī ||
The steadfastness by which a dull-minded person refuses to let go of sleep, fear, grief, despondency, and conceit: that steadfastness, Arjuna, is of inertia.
Modern context
Tamasic steadfastness is the stubborn refusal to let go of sleep, fear, grief, despondency and conceit. It is a strange kind of firmness: holding on tightly to what harms. Many people are remarkably steadfast in their worries, grudges and gloom. That firmness would be better spent elsewhere.