While internal motivation is by far the best motivator, a little accountability can go a long way. Accountability leads to other people encouraging, suggesting, and asking about your book Their interest and support (or skepticism) can be powerful prods to keep you writing.
These people can be perfect strangers. I go out and work in a deli two days a week and a bookstore once a week. I carry around a stuffed writing buddy with a nifty t-shirt. Writers recognize it and ask what I write and share their own projects. Strangers ask what the t-shirt says or comment on how cute the squirrel is and I can say that it’s my moral support while I work on a book. A week later, these people stop by and ask how my book is going, tell me about books they have read, or ideas they have had for my book or one of their own. One kid started writing his own book and stops by every week to tell me about it. So fun!
These people can be family. Family can probably be the most trusted to get onto you when you don’t meet your goals, to let you ramble on incessantly as you try to hammer out some minute detail, or a shoulder to cry on after you’ve killed a character. Family also tends to be skeptical that you really will finish your book so there’s the added incentive of proving them wrong. I know it took me almost a year to prove to my family that I was serious about it.
These people can be other writers. There are many writing networks out there. Who better to cheer you on, offer encouragement or commiseration, and sage advice than writers at your level of experience, those with more experience, and those with less? You can even tailor your interactions to your needs for time, privacy, and support. There’s library groups, professional groups, social media groups. When you form a connection with someone, there can be emails, phone conversions, and face-to-face encounters.
This person can be yourself. Make goals, post them where they are clearly visible, and track your progress (or success and failure rates) to get a realistic idea of your progress.
The point of accountability is to gain outside support and motivation for your writing effort. Sometimes that little extra push that comes from expectations is all you need to keep going.