Nathan Bransford in his post providing 'five ways to stay motivated while writing a novel:
Develop the idea that you’re letting yourself down if you don’t finish it. Put pressure on yourself. Be afraid the regret you’ll feel the rest of your life if you don’t accomplish your dream. Fear is a feeling that can keep you going.
It sounds dramatic, counterproductive perhaps, but there is nothing quite like the possibility of failing to keep you motivated.
I was terrified that I wouldn't finish my novel. So scared in fact that, at some point, it became unthinkable. I knew that I just couldn't let it happen.
I mean, how could I not complete something that I'd already spent so much time and energy working on? What would my family and friends think if I were to give up halfway through? No. Not me. I had to finish. When the going got particularly tough, fear of failing saw me through.
However, you might argue that motivation is better found through more positive sources, like the glittering prize of publication. That's probably fair enough, but what if you do fail? Is it just a case of okay, never mind, on to the next thing? Or is there some kind of mental forfeit?
Aiming to succeed is hugely motivating, but not wanting to stuff things up can get your juices flowing and help you focus just as much, if not more so.