I grew up with a father and a brother who were very manic and then depressed following a football team that would lose more often then not. So, it is interesting to see the similarities with the manicly depressed. The mind is, well, a tool, and people go through these feelings, the depression and the joy and learning and learning and growing, each step of the way. Without hardship, so little is learned. I traveled to Jamaica and saw "poor" people, and could not believe how very, very "rich" these people are. A humbleness, a love, an understanding, and pride, that the youngest children learn. A kindness taught that could not be taught if everything was given to them, ie, violent video games, computers, tv, money. The depression people feel, when they want something that they think will make them happy....but I say to them, you just don't know. It all is pretty deep for me, and I'm not the smartest person in the world. But, as for myself, I like the idea of the disease of manic-depression being compared to football, then things seem more in control, and perhaps simply by changing the words we use, our outlook, we can see the small flame burning from the candle, in the darkness, and the flame not as small as we thought.
The quote you gave seems to me like Christian Science, mind over matter. It's all in the head. But there is more than the mind. There is more than the good and the bad. There is love that helps everyone, no matter your position, and it is difficult to explain, in words.