I've learned, though, that when Cynthia is in a low time (her incidents of depression are very irregular and unpredictable, so the difference between her "up" days and her "down" days are very dramatic), her whole thinking process changes. The best analogy I've thought of is that it's as if a person has a disease that periodically affects their brain so that they can no longer see the color green. When the person is "normal", they can see fine, but when the disease affects them they can't see the same. They even know mentally that green still exists, but that knowledge isn't helping them because, as I've heard said, "perception is reality". They're not comforted by someone assuring them that green objects still exist the same as ever, they're not encouraged by pressures to "meditate on green objects", and they're not helped by advice to "just concentrate on the green that you can see". In that moment, until something changes, green doesn't exist for them.
In my analogy, green is encouragement, or hope. When Cynthia is in a "down time", the same motivations, encouragements, and passions that drive her when she's "up" don't even exist for her, and encouraging her in the same way that I could encourage her normally just doesn't work. That's why most depression advice I've read (and I'm no expert, I'm just generalizing) doesn't help much: most of them are the same ways that we can all encourage ourselves when we feel discouraged. Those ways work great when the problem is just that the green we can see is getting crowded out temporarily by all the blue and red objects in our lives. The problem is that depression fundamentally changes a person's perception: if it's impossible to see green anymore, you have to get back to normal sight some other way, other than just "seeing different". Just like that, depression requires more than just "thinking different".