[ From Pompi Pompi Development Blog ] 

I had a rough time the last week. Some stuff related to my game were frustrating me, and some difficult events at work. The thing is, a week ago I had a lot of motivation and everything was going fine and smooth.
I am not sure this is accurate or the absolute truth, but there seem to be a matter of inertia in motivation and developing a game. If you are already feeling good about working on your game and you are excited about it, its easier to keep on doing it. However, something like events related and not related directly to your game, could stop your wheel from rolling. After you stopped developing and doing the stuff you enjoyed doing, suddenly its very difficult to get back to it.
I was too lazy to work on my game, even though I knew that two weeks ago I had a lot of fun doing just that. Then I told myself what I have already learned from these kind of situations, you have to force yourself to work on your game. Even though its boring, you have to start pushing the wheel, and its hardest to push a standing wheel.
But it didn't help, I was still too lazy to do it. Then I had thought to refine this "force yourself" method. I know it worked for me before, but now its not working. The refinement would be, start with the easiest things at first that would motivate you. Such as writing this blog(another good reason to write development blogs). Another thing is to have others set deadlines for you. For instance, if you work with a sound guy, you can decide that you have one month to complete the sound effects. Soon he will be sending you sound effects and you will have to work on them, because you have set a deadline.
We can learn from this that not all the things have the same difficulty when you are unmotivated. And if you see that you are too lazy to do something, it doesn't mean you can't do anything. You just need to find easy things to do first, soon you will start catch up and do the harder stuff as well. Finding external motivators can also help, such as having someone you work with set up a deadline to force you work on stuff. And eventually, remember that starting is the most difficult part, and after you start it will soon become easier. Although you have to remember this might be more complicated, but it might still help you thinking about it.
I will be glad to hear about your own experience and your own insights.