Not their fault, but the result of evolutionary change to bring variation and viability in the population. Personality of human beings reflects in their behaviour in the society such as interaction with fellow beings, doing daily activities, doing competitive works etc. According to researchers, human beings belong to three classes based on their behaviour. Type A behaviour also called TAB personality is characterized by the competitive attitude and enthusiasm. So most of such personalities are workaholic. They can be referred to as Stress Junkies because they are always concerned about the job. Type B personalities on the other hand are generally patient, relaxed and easy going. The AB personalities show a mixed behaviour and they cannot be clearly categorized as either Type A or Type B personality.
Type A individual are ambitious, aggressive, controlling, highly competitive, impatient, and time conscious persons.Type B personality is almost perfect when compared to Type A personality. They are generally patient, relaxed, easy going, lack overriding, sense of urgency etc. Type B personality is apathetic and are disengaged persons as experts says. They often do jobs silently without showing much stress. Competitive mentality and sense of impatience are less in Type B persons.
AB personality is a hybrid behavior showing both Type A and Type B characteristics. They have mixed profiles and difficult to categorize as Type A or Type B persons. Health psychology studies say that the mental health and physical health are closely related. But still there are controversies among psychologists and researchers to classify personalities based on sample data and merely observing behavior. Some researchers have the opinions that, the personality can change due to learning, social behavior and also due to the changes in the living environment and life styles.