Scientists once believed that high-energy, aggressive people\u2014so-called type A personalities\u2014were more at risk for stress-related disorders than others. But that has proven not to be the case. In fact, some type A\u2019s enjoy stress and see it as a positive. In effect, they simply don\u2019t experience what we know as stress."Competitiveness does not damage your health," says psychologist Sue Parkerson Wisner of the Duke University Medical Center. Only type A\u2019s who get angry or depressed have stress-related health problems, she says.Type A\u2019s who don\u2019t turn the steam inward have proven to be more like zebras than humans in their response to stress, a famous analogy first posed by stress researcher Robert Sapolsky in his 1994 book, Why Zebras Don\u2019t Get Ulcers. When faced with a threat, such as a lion springing from the bush, zebras have the same fight-or-flight response as humans. But when it\u2019s over, when their brothers and sisters are now lunch and the lions are settling down for a snooze, zebras stop worrying until the next time the lions show up. So they don\u2019t die of stress.Psychologically healthy type A\u2019s behave the same way. When that big meeting is over, they leave their stress in the conference room. They don\u2019t worry about the next big meeting until the lions wake up.