[tetha]

This sounds consistent with what I am understanding so far.

To my current understanding, it is necessary to distinguish between a state of mind and a current mood. Certain states of mind just don't support certain moods. Furthermore, for certain states of mind it's hard to get into and hard to get out of.

As a silly example, note my daily life. If I sleep in hard, I'm just not in a productive state of mind and I don't get out of that state of mind all day. The result is that I just don't do much that entire day. On the other hand, if I set my alarm clock to 6 in the morning, I get all my chores done to 10 and pull a full workday on hobby projects without breaking a sweat. The "zone" of programmers also appears to be such a state of mind which just doesn't support social interactions well.

Depression appears to be similar to this. It's a state of mind that's hard to get out of (or hard to cover up even) and that just doesn't support cheerful and happy moods. From there, our usual stress avoidance mechanisms kick in, for example by avoiding overly cheerful or happy people and things don't improve much.