High Quality Content by WIKIPEDIA articles! The trait of extroversion-introversion is a central dimension of human personality. Extroverts (also spelled extraverts) tend to be sociable, assertive, and interested in seeking out excitement. Introverts, in contrast, tend to be more reserved, less outgoing, but are also marked by a richer inner world. They are not necessarily loners but they tend to have smaller circles of friends and are less likely to thrive on making new social contacts. Introverts are less likely to seek stimulation from others because their own thoughts and imagination are stimulating enough. The terms introversion and extroversion were first popularized by Carl Jung. Virtually all comprehensive models of personality include these concepts. Examples include Jung's Analytical psychology, Eysenck's three-factor model, Cattell's 16 personality factors, the Big Five personality traits, the Four Temperaments, the Minnesota Multiphasic Personality Inventory, the Myers-Briggs Type Indicator, and Socionics. Extroversion and introversion are generally understood as a single continuum. Thus, to be high on one is necessarily to be low on the other.