伝説のスイスの精神科医であり精神分析医であるカールユングによると
According to Calr Jung, a legendary Swiss psychiatrist and psychoanalyst, no one is truly extrovert or introvert. They must have had their second nature. However, some tend to be extroverted or some tend to be introverted. This tendency then forms different skill sets for the two, including their emotional state and how to deal with them.