[peterkelly]

Clinical depression is often a result not of one's external environment or social situation, but a chemical imbalance in the brain (Serotonin in particular). I'm certainly no expert on the topic, but from what I know science still doesn't have a definitive answer to what brings such an imbalance about. Also it is sometimes hereditary.

External factors (financial/relationship problems and the other various pressures of life) can contribute to the problem and either be a trigger for or worsen the symptoms. But there are many instances in which someone who is otherwise successful and happy with things in general (as it sounds like this man was) can suffer from it. Everything can be going fantastic in your life, but the "black dog" comes visiting nonetheless.