I ask people about their projects and the answer I get is always (or almost always) the subject of the project.
Sometimes I ask specific questions like "what kind of project? Is it a dissertation? A thesis?"? And still the answer I get is the subject of the project.
But your project is not just about a subject, it has a certain form.
If you can see that form, and understand how that form relates to the work you're trying to accomplish, then the writing process becomes much easier. I've mentioned this in an earlier blog entry.
Of course, form is uncertain in someways--we cannot be certain that what we think will be a good dissertation will be thought a good dissertation by a professor--but it is still useful to have some image of the complete project.
By having some idea of the complete project, we can judge when we need to do more work, and when we can move on to another section/chapter.
If you don't have an idea of the complete work--an outline, an estimate of length--then you can more easily waver--should I add this? should I add that?
Well, there are lots of people who use outlines while writing, and that helps a huge amount. But in general, people, or at least people who are stuck, don't think about the general form of the written project as much as they do about what they're trying to say.
There's another angle that people think of less often. The audience. Understanding your audience is crucial. By understanding the audience, you understand what needs to be said.
When you're writing a dissertation or thesis it can help to think about writing to two audiences. One is real, the other imagined. The real audience is your committee. You want them to sign. The other is the audience that you would hope for the work at a later date.
The general point I'm making here is that there are several perspectives one might take on a work, and by understanding more than one, your writing process can benefit as the additional insight into the project from different perspectives provide guidance towards completion.