Enthusiasm gets me off my duff: Commitment keeps me going, when the going is rough.
I usually hate or am bored with a quilt somewhere in the middle of the process. Since I am a "budget quilter" I have to finish them from start to finish, and I often am stuck when the piecing is done and the quilting itself is called for, since that is my area of least competence. I am curious how the thing will look when sewn together, so that keeps me interested during the piecing process, and that is often a surprise too-how my imagination had it missed. (Sometimes I am pleasantly surprised at the secondary patterns that emerge) I usually have to set a top aside and stew over it for quite a while to come up with a quilting plan- I call it "the creative stew." Then I have to reenter the arena, pick it up, and carry out the quilting idea that emerges. Deadlines often help with this.
No matter when I finish, I am usually pleased with the end result - and that keeps me going onto the next project(s).