We need time to relax and enjoy ourselves too, no matter how dark the story. The occasional humorous moment helps with that. That's one of the things that Joss Whedon excels at in his storytelling.
Patrick RothfussHowever, while being able to think about two things at the same time is a terribly convenient, the training it takes to get there is frustrating at best, and at other times rather disturbing. I remember one time I looked for the stone for almost an hour before I consented to ask the other half of me where I'd hidden it, only to find I hadn't hidden the stone at all. I had merely been waiting to see how long I would look before giving up. Have you ever been annoyed and amused with yourself at the same time? It's an interesting feeling, to say the very least.
Patrick Rothfuss