For the Epicureans, ataraxia was synonymous with the only true happiness possible for a person. It signifies the detached and balanced state of mind that shows that a person has transcended the material world and is now harvesting all the comforts of philosophy.
For the Pyrrhonians, owing to one's inability to say which sense impressions are true and which ones are false, it is a pleasant place that arises from suspending judgment on dogmatic beliefs or anything non-evident and continuing to inquire. The experience was said to have fallen on the painter Apelles who was trying to paint the foam of a horse. He tried and failed so many times that in a rage he threw a sponge he was cleaning his brushes with at the medium and thus produced the effect of the horse's foam.