Why do the traits of introversion-extraversion keeps surfacing in some of the theories; for example, as first seen in Jung's theory,and also in the Big Five theory, and Eysenck's theory?
Personality traits are researched, explored and researched by scientists in an effort to explain the particularities personality and in order to provide answers to difficulties experienced in the plethora of disorders that have been identified over the years. Carl Jung first introduced the concept of introversion and extroversion as opposing orientations interaction of personality with the world: extraverts are focused dominantly on interacting with external experience while introverts are focused dominantly on interacting with internal experience.
The difficulty with studying behavior is that it is subject to many external factors that alter reactions, sometimes quite drastically, preventing relative measurement, and sometimes only marginally, allowing for comparison and collection of data. Therefore, the study of personality continually evolves, particularly in view of modern advancements in brain and cognitive science. One thing that doesn't change is the component of personality that interacts and the degrees to which that interaction is external or internal. This is why extraversion-introversion continues to be a foundational part of personality theories: all personalities interact with internal and/or external stimuli and motivators and do so in varying styles and to varying degrees.
Eysenck's theory considers the introversion-extroversion dimension and what is called the neuroticism-stability dimension. Jung's theory contends that an individual whose primary function is to be extrovert has a secondary function which is introverted and vice versa, and the single continuum of many theories maintains that one function is dominant and the other therefore latent or suppressed, thus further deepens the discussion.
In a westernized culture, extraversion is encouraged and seen as a measure of success whereas studies show that, in fact, academically, it is introverted people who are more successful. Extraverted people are considered to be happier but in fact that is because they exist in an external world where satisfaction comes from others whereas introverts find their satisfaction in more subtle ways and thus others are not aware of their happiness levels, as they have less need to share their contentment.
As extroverts and introverts do not always behave typically, this further raises questions for discussion. Previous models are being updated constantly and the "Big Five" theory of extroversion, agreeableness, conscientiousness, neuroticism and openness to experience or intellect has been accepted as relevant to personality and as a positive step towards refining the concept of factor analysis, defining the most important factors in the approach to behavior and personality.