Danny Elfman, while Jack's trying to figure out Christmas in his tower: "'Jack's Obsession' and 'What Have I Done?' were always going to be the sister songs, the companion songs, in the sense that each one starts low and he works himself up to a frenzy. So, the fun of those two songs is that in each of these songs, he works himself up--in the singing of the song, he's going to work himself up into a complete clarity, or at least what he thinks is clarity, and, uh, go from, in 'Jack's Obsession', just a state of kind of down, kind of, uh, how do you explain the way Tim explained it to me--he's, he's not eating, he's down, he's like, he's just depressed over this thing, he can't figure it out, he really wants to and until he does it's gonna drive him crazy. And he finds it in the song. And he works himself up into a complete frenzy of enthusiasm. And, of course, in uh, 'What Have I Done?' he starts with 'my life is over'. He's starting from a state of real depression. 'My life is over, I've ruined everything.' And in the context of singing that song convinces himself, 'No, I haven't! And it's all great! And I'm gonna fix it! And it's fantastic!' So both of them have that element of starting low, and he's gonna completely convince himself, which is the thing I love about Jack, is, nobody convinces him of anything, he convinces himself in his own storytelling. And works himself up into these frenzies of clarity and enthusiasm and, uh, get up and go."
And while Jack's in the graveyard after his sleigh's been shot down: "So here, Jack has one song's length of time to work himself from the depths of despair to the heights of enthusiasm because Jack is the ultimate manic in that way."
Henry Selick, during the "Jack's Obsession" scene: "I love how he rallies himself. Um, I think there's a lot of Danny Elfman in that particular song. He just, by himself, with his own ego, and his ability to sort of, just, like, just turn things around. Pride--whatever it was. I just, I love that. No one else has to tell him. He--he's his own worst enemy and his own best friend at the same time."