There are scenarios where there is not a clear cause that is within the person's control. Granted, I think your suggestions are great places to start, and helpful for many. That said, some cases of depression cannot be effectively treated without therapy or medication, and I think it's a bit... incomplete to suggest otherwise.
No one knows that until they've exhausted other options.
Hope is not a bad thing, unless you want to sit around and do nothing with your life and feel terrible. To be concerned with the impossible is a symptom and a cause of depression, called learned helplessness.
