One student had (I still can’t believe this) 22 partial novels. Amazing. By “partial” I mean he’d written more than a single scene or chapter. His partials all had more than four chapters; some of the novels were a few thousand words short of done.
Writing fiction becomes easier with practice
After you do something once (tie your shoelaces, create a budget, drive a car) repeating the action is easier — you know how to do it. Do something ten or 20 times, and the activity becomes easy for you. Do an activity 100 times: it’s become habitual.
This means that if you give up on a novel once, you’re more likely to do it again. Equally, complete a novel once or twice, and your creative self takes the “I’ll finish this” concept on board.