Trace it back, and the source will always be fear. The source cannot be anything other than fear. To conquer your anger, you must conquer the fear at the source of that anger. For if you fail to conquer the fear, the anger will continue to manifest. Chronic depression is not a form of fear.
Chronic depression is a local chemical condition.
The key seems to be assimilation or avoidance, but it isn't. The key is acceptance. The fear which always lives within you is the fear you are inadequate. Your life is a struggle to conquer fear. Fear can only be conquered when you are about to fail, or fail.