Starting with quotes from book 3 "The 3rd Degree". Page 13
"A house without music," her mother used to say, "is a house without life."
From '6th Target' at the beginning of chapter 55, page.139
I drove toward San Francisco General, my mind swirling with terrible, sinking
thoughts. Claire once told me this thing about brain chemistry, the nub of
it being that when you're feeling good, you can't ever imagine feeling bad
again. And when you're feeling bad, it's impossible to imagine a time when
you won't be circling the drain.
I'm not sure about the first part because I know what it's like to be laughing and yet still have a black pit inside of you. The second part makes sense to me though. When you are feeling down what really gets you is when you have no hope of the situation getting better.