"Both Indian and Greek philosophers held the highest ethical good to be an attitude which regards with the same emotion or valuation those events which are to one´s personal worldly advantage — such as pleasures and fulfilled intentions — and those which are not — such as pains and frustrated intentions. Various terms are used for this mental stance, from the Greek ataraxia to the Sanskrit upeksa — both of which may be translated as “imperturbability”. The ethics of imperturbability involves an attempt to get one´s mind beyond the fluctuations of pleasure and pain. There are two approaches, one transcendentalist, the other naturalistic. To attain such an attitude is to disengage oneself from the ordinary patterns of motivation. In some contexts the disengagement is precribed in order to promote a transcendentalist motivation. Sensations are considered unreal in comparison with some other hypersensual realm; the goal is to become “dead to this world” (impassive, impartial, equanimous, indifferent) in order to gain access to higher Being. This transcendentalist approach is found in Platonism and Neoplatonism, the Vedanta, and most schools of Mahayana Buddhism. In other contexts, such as Theravada Buddhism and Epicureanism, this-worldly experience is accepted as what is given to deal with. Imperturbability is advised not in hopes of attaining a transcendental viewpoint but on naturalistic grounds, in response to the uncontrollability of experience."
— Thomas McEvilley
, The shape of ancient thought