Bhagavad Gita 18.25
अनुबन्धं क्षयं हिंसामनपेक्ष्य च पौरुषम् । मोहादारभ्यते कर्म यत्तत्तामसमुच्यते ॥
anubandhaṃ kṣayaṃ hiṃsām anapekṣya ca pauruṣam / mohād ārabhyate karma yat tat tāmasam ucyate
Translation
Action begun from delusion without regard to consequence, loss, harm, or one's capacity, is called of the dark kind.
Reflection
Which recent action did you launch without checking consequence, cost, harm, or your own capacity?
Read this verse in its chapter: Chapter Eighteen
Tamasika karma. Four blind spots, listed. Anubandha, downstream consequence, not factored. Kshaya, what will be spent or destroyed, not factored. Himsa, the harm caused to other beings, not factored. Paurusha, one's own actual capacity, not factored. The act is launched from moha, a fog where none of these are visible. The dark act is not always the loud one. Often it is the deal taken without thinking through, the post that ignores who will be hurt, the project begun in haste because boredom needed feeding. Notice the diagnostic. If reflection is absent in any of these four directions before action begins, that act is tamasika regardless of its surface respectability.