How does depression develop?

Many of us experience day-to-day changes in mood. It's normal to experience disappointment when we fail at something or lose something. Most people who go on to develop depression can recall some important disappointment before the episode began. They have “down feelings” that don't go away after a few days, and they get progressively worse. Other folks have a harder time pointing to any specific thing that started their depression. Sometimes our bodies have challenges related to our chemistry that can make a person more likely to feel depressed.