Bhagavad Gita · Chapter 18: Freedom through Renunciation

Bhagavad Gita 18.25

anubandhaṃ kṣayaṃ hiṃsāmanapekṣya ca pauruṣam | mohādārabhyate karma yattattāmasamucyate ||

An action undertaken out of delusion, with no regard for its consequences, for loss, for harm to others, or for one's own capacity, is said to be of inertia.

Modern context

Tamasic action is undertaken carelessly, without regard for consequences, for loss, for harm to others, or for whether one can even do it. It is reckless action. Starting a fight one cannot win, making a promise one cannot keep, acting without thinking of who will be hurt: all are tamasic. The verse is a checklist worth running before any big decision.