Envy is an emotion which "occurs when a person lacks another's superior quality, achievement, or possession and either desires it or wishes that the other lacked it". Aristotle defined envy as pain at the sight of another’s good fortune, stirred by “those who have what we ought to have.” Bertrand Russell said that envy was one of the most potent causes of unhappiness. Not only is the envious person rendered unhappy by his or her envy, Russell explained, but that person may also wish to inflict misfortune on others, in forms of emotional abuse and violent acts of criminality.