The author fails to differentiate quite a few things here. Long-term depression is a way of thinking and feeling that some people fall into easier than others

The author fails to differentiate quite a few things here. Long-term depression is a way of thinking and feeling that some people fall into easier than others and that is also cultivated over time. If you had a rough childhood and coped with it by getting sad and finally dissociating from your emotions in an early age, and you proceed to do that for a long time, then you are likely to get what's called a major depression. I don't know if I would call that a symptom or a disorder and I frankly think that most of the time it doesn't matter for the treatment.