Bhagavad Gita
18.25

अनुबन्धं क्षयं हिंसामनपेक्ष्य च पौरुषम् | मोहादारभ्यते कर्म यत्तत्तामसमुच्यते ||

anubandhaṁ kṣayaṁ hiṁsām anapekṣya ca pauruṣam mohād ārabhyate karma yat tat tāmasam ucyate

Translation

Action undertaken out of delusion, without consideration of consequences, loss, or harm, and without regard for human capacity — that is declared tamasic.

Interpretation

Tamasic action: begun out of pure delusion (moha) without any consideration of consequences (anubandham — consequences, implications), without regard for the loss it might cause (kshayam — destruction, waste), without caring about the harm it might inflict on others (himsa), and without realistic assessment of capacity (paurusham — without considering whether one actually has the ability to accomplish it). Tamasic action is reckless, thoughtless, harmful, and deluded. It is action without wisdom, effort without understanding — and it always produces suffering.