An action undertaken from delusion, without considering the consequence, the waste of resources, the harm it may inflict, and disregarding one’s own capacity, is said to be tāmasa.
Tāmasa action, points Krishna, is blind and cyclonic in its effects. Tamo-guna always clouds the mind and intelligence. As a result, the one under its influence thinks not about the relevance and consequence of whatever he takes up and pursues. He cares to think little about the harm, chaos and waste his action involves.
A tāmasa person is given to act with expectation, and is impatient to get the fruits thereof, no matter whether it harms anyone. To finish the task is the only concern he has and cares for, because of his sa´ga (delusional clinging) to the fruits.
Often the action he undertakes is beyond his potential and scope. He wants to bite off more than he can chew. Blind hopes about gain and success overpower him so much that nothing deters his execution. Delusion and deluded actions dominate his thoughts, feelings and aims.