When internalized, an emotions stops functioning in the manner of an emotion and becomes a characterological style. You probably know of someone who could be labeled 'an angry person', or someone you'd call a 'sad sack'. In both cases the emotion has become the core of the person's character, her identity. The person doesn't have anger or melancholy, she is angry and melancholy. Every human being has to contend with certain aspects of this process.
Internalization takes place when all three processes are consistently reinforced.
We always have the need to identify. Identification gives one a sense of security. By belonging to something larger than ourselves, we feel security and protection of the larger reality. The need to identify with someone, to feel a part of something, to belong somewhere, is one of our most basic needs. With the exception of self-preservation, no other striving is as compelling as this need, which begins with our caregivers or significant others and extends to family, peer group, culture, nation and world.