Ego/willpower depletion - The Wikipedia article on ego depletion is pretty good. Basically, a lot of recent research shows that by doing something that takes significant willpower your "battery" of willpower gets drained some, and it becomes harder to do other high-will-required tasks. From Wikipedia: " In an illustrative experiment on ego depletion, participants who controlled themselves by trying not to laugh while watching a comedian did worse on a later task that required self-control compared to participants who did not have to control their laughter while watching the video." I'd strongly recommend you do some reading on this topic if you haven't - Roy Baumeister has written some excellent papers on it. The pattern holds pretty firm - when someone resists, say, eating a snack they want, it makes it harder for them to focus and persist doing rote work later.The Cognitive Cost of Doing Things
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.