This list can go on and on...
It varies from person to person. Many people need counseling but some are too prideful to get some (like me lol). Some people have chemical imbalances that leads to it and they definitely need a doctor.
It is a very debilitating experience that requires a great deal of strength and will to overcome. I've struggled with it for years, I'm nowhere near as depressed as I used to be but I still relatively am. Some of the things that helped me are exercise, taking care of myself, traveling, breaking down long term goals into small ones so you can feel accomplished more often, inspirational/motivational quotes/videos, generally trying to be optimistic, etc. It doesn't go away overnight, it's a day by day process.
To whoever still struggles with major depression: The seemingly endless stormy and cloudy days will eventually make way for a vivid sapphire sky shining on a stronger and wiser person :)