Neither the environmental event nor the persons response defines stress, rather the individuals perception of the psychological situation is the critical factor. According to Lazarus, the effects that stress has on a person is based more on that persons feelings of threat, vulnerability and ability to cope than on the stressful event itself. He defines psychological stress as a "particular relationship between the person and environment that is appraised by the person as taxing or exceeding his or her resources and endangering his or her wellbeing.