Solitude and isolation. Dwelling on problems for long periods of time. Not being satisfied with life as usual. Preferring to think before (or instead of) acting. Taking a long time to complete a seemingly simple task, because you can see the full ramifications of the task and how difficult it really is. Concern with the abstract and the illusionary/visionary instead of the immediate. Some of the attitude towards focus and concentration, although that varies.

In short, I think that depression can be somewhat characterized as a sensitivity to, or inability to filter out, certain perceptions, especially abstract concerns. What the author is advocating seems to be a conscious effort to seek those perceptions. My opinions are, of course, biased by my own experiences.

As someone who's experienced depression, I still don't see the connection between depression and any of the things you listed.

I do. However, I think it may be superficial. I do not think depressed people are overall as successful as the true leaders are, common sense says they may be less successful than the general population.

Maybe I'm more broken and depressed than I thought, since the isolation, solitude, dissatisfaction, thoughtfulness, and so forth all remain with me even when I'm not feeling down.

Just out of curiosity, what culture are you living in or where did you grow up? The definition of depression varies from culture to culture and I'm interested in understanding how your cultural background is influencing your perception.