Sebastian Marshall's Lifehacker post on the cognitive cost of "doing things" is a really interesting look at all the hidden "costs" that keep you from doing stuff, and that you pay when you make stuff happen. I'm especially interested in "activation energy" — "starting an activity seems to take a larger of willpower and other resources than keeping going with it," particularly this: "Things like having poorly defined next steps increases activation energy required to get started." I get a lot email asking me to help out with stuff, and I certainly notice that the more nebulous the request is, the more likely the email is to sit in my inbox for days or weeks as I try to figure out what to do about it. I'm certainly going to keep this in mind the next time I try to get someone else to do a favor for me.
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.