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 RothfussShe taught me I should never do anything in private I did not want talked about in public, and cautioned me not to talk in my sleep.
Patrick RothfussSometimes when I get up after writing, I'm surprised at how my body feels. Suddenly I'm not a lanky, hungry young boy any more. It's no fun putting on ten years and fifty pounds all of a sudden. Other times, I get up and I'm pleasantly surprised that I'm not a weary innkeeper, hopeless, with bones that feel like they're made of lead. I really sink into the characters that I write.
Patrick Rothfuss