Both terms indicate extremes of personality, but in general people fall somewhere in between.
Prefers to be alone or with close friends. Does not like large parties and gatherings. Thinks deeply about life. Prone to anxiety, which may cause over absorption.
Enjoys society and company with new people. Does not think too deeply about life, but does find talking easy. May find difficulty with a lasting relationship, such as marriage, which could cause insensitivity.
The solution to problems of being over introvert or over extrovert can be found in developing the opposite style of life. A person who is anxious would need to spend time talking to many sympathetic people. A person who finds difficulty with a lasting relationship would benefit from self analysis and time spent with an introvert.