joshua, let me tell you, I've felt this too.

If I had to guess, it springs from not becoming bored with the project, as much as, with any project there are a number of problems. Some of the problems take a lot more creativity and challenge the programmer more, than others. At the very least, I've found this to be true with me, where the interesting problems, could be considered your dessert, and the rest of it, your dinner (be it documentation, or other simple, but often mind numbing tasks.)

So I find myself going back to what my parents said, "Finish your dinner, or there'll be no desert." Put in stubs for the functions that you most want to write, and leave enough in the comments that you can remember what you wanted to do. Then, eat your dinner so to speak.

Hope this helps,
abitkin