I'm fascinated by psychology and think my understanding of it helps me with character development. One thing I find intriguing is that many of my favorite writers have a background in this subject.
A few years ago, I took a course in developmental psychology. It introduced me to several theories about how the personality of an adolescent emerges. One I found particularly interesting was that of Canadian psychologist James Marcia, who says that there are four identity statuses. To understand these, you need a couple of definitions:
Crisis: The period of identity development when a person is choosing between various alternatives, trying on different skins.
Commitment: A personal investment made when an individual chooses what to do with his life.
The four identity statuses:
Identity diffusion: The state in which an adolescent has not yet experienced an identity crisis or demonstrated commitment. A sort of blissfully ignorant and unaware position that is the standard before the individual begins to examine his life and values.
Identity foreclosure: The state in which an adolescent has made a commitment without experiencing a crisis. Example: a person adopting his parent's religious beliefs without examining them for himself or questioning them in any way.
Identity moratorium: The state in which an adolescent is in crisis, but has not yet defined his commitment, or has defined it in only a vague way. Example: an individual who bounces from subject to subject in college, never deciding on a major, or continually changing her major.
Identity achievement: The state in which an adolescent has undergone crisis and made a commitment. Example: a person questioning the beliefs of the church he was raised in, exploring other religions, and deciding that he agrees with the values of his own faith after all.
I think limiting these statuses to teenagers is shortsighted. Many adults never go beyond identity foreclosure, while others are forever mired in identity moratorium. I also think you can have a crisis, make a commitment, then find yourself back in crisis.