Tamas

 In the Samkhya school of philosophy, tamas (Sanskrit: तमस् tamas "darkness") is one of the three gunas (or qualities), the other two being rajas (passion and activity) and sattva (purity, goodness). Tamas is the template for inertia or resistance to action. It has also been translated from Sanskrit as "indifference".

The nature of Tamas

Sattva, Rajas and Tamas is seen in various facets (including dietary habits) of Hinduism, Buddhism and Sikhism, where tamas is the lowest of the three. Tamas is a force which promotes darkness, dissolution , death, destruction, ignorance, sloth, and resistance. Tamas is also a Guna or Quality that is much needed to counter Evil, as an example Bhairava Incarnation of Lord Shiva is a Tamasic Avatar, and Lord Shiva Himself out of the Trinity represents Tamas, where Shiva drinks the poison of his devotees to get rid of their sin, hence absorbing the Tamo-Guna of devotees, in Devi worship, there are many goddesses which incarnate within the Shakta sect of Hindusim where goddess are offered animal sacrifice.

In the holistic-universal creation Tamas is where the demons and asuras dwell, their energy is purely tamas. Since Tamas can't be controlled by mortal energy, vedic philosophy dictates Sattva as the preferred guna.

The gunas are defined and detailed in Samkhya, one of the six schools of classical Indian philosophy. Each of the three gunas has its own distinctive characteristics and it is believed that everything is made up of these three. Tamas is lowest, heaviest, slowest, and most dull (for example, a stone or a lump of earth). It is devoid of the energy of the rajas and the brightness of sattva.

Tamas cannot be counteracted by tamas. It might be easier to counteract it by means of rajas (action), and it might be more difficult to jump directly from tamas to sattva.
Occurrence of Tamas

The Bhagavad Gita says,

    Once a man, having sattva as his main habitual behaviour, feels that it is not easy to live in this world by the means of sattva, he will start being Rajasic. As per rajas, the man starts habitual working thinking only of what he wants. It becomes hard for him to think about his Karmic actions as good (satkarmi) or bad (akarmi). Then, he feels good in giving harm or any of bad feeling to other peoples. He then thinks, how can I provide harm to others and attain my goal. This behaviour is under control of a power in this nature called mohamaya and brings about asakti (Sanskrit: Āsakti – selfishness).

(originally "darkness", "obscurity") has been translated to mean "too inactive" or "inertia", negative, lethargic, dull, or slow. Usually it is associated with darkness, delusion, or ignorance. A tamas quality also can refer to anything destructive or entropic. In his Translation and Commentary on the Bhagavad-Gita, Maharishi Mahesh Yogi explains "The nature of tamo guna is to check or retard, though it should not be thought that if the movement is upward tamo guna is absent".