I'm very responsible when I'm writing a tech book or article under contract. I have a deadline, my editor is expecting my work, and I turn it in on time. Sometimes I put it off a bit, but I pride myself on making deadlines, and I will do whatever is necessary to do so.
But without this external motivation, when I'm writing for myself, I don't have the same urgency. It's too easy for me to tell myself that I'll do it later. What I need is a deadline for my novel, or parts of my novel. How can I simulate that same sense of urgency in a way I can take seriously? Just promising myself isn't good enough.