Depression is probably the most common emotional problem anyone will encounter. Its a feeling of sadness, discouragement, and an inability to get "on top of things."
The Psalmist said the cause of depression was sin, according to Psa. 38:38. Out of a sense of failure or inadequacy (even caused by small things) the person begins to dislike himself or herself.
This is may be projected to a distrust of God, resentment of others, and self pity, which leads to feeling more guilt, further depression, more inactivity, doubting, complaining, and worrying so that he or she feels more a failure, more guilty, and more depressed until you feel as though your in an inescapable pit (James 1:14-15)