If you continue to write a novel, it will one day be written. While your novel is half-written, ideas for new novels may poke into your head. You will tell yourself that these ideas are easier to write, and thus you should abandon your first half-written novel to work on your new idea. However, you just realize that what you thought was easy turns out to be hard, for there are few good novels without finely crafted twists and turns that required a lot of mental preparation on the part of the author.
Discuss.
Bookshelf Battle 
It happens. Has happened to me. But, I always ended up going back to the previous novel, as I felt awfully guilty. It’s like murder, in a way, you know – leaving a novel to starve just to water ideas for another novel. No, no, sport.
One reason I am glad an opus(a cartoon) takes about 90 minutes from thought to finished product , not months or years. Have lottsa ideas brewing simultaneously but just do a 1 minute sketch to refine later fpr such and focus on present drawing/joke.
Opus the Penguin?
I actually recently did this – took a break from my novel (which had stalled) and started working on a new project which was in a totally different style and genre. And it was fun! After about 4 months or so of playing in this other world and not stressing about the other novel at all I suddenly realized *exactly* what I needed to do to fix what was going wrong with my main project and returned to it with gusto. I think sometimes novels need a little room to breathe and marinate, or at least mine do! And now I have the start of another project for the future – win win.
Well that’s good to know that occasionally this practice has a happy ending.
This is why I have a pile of notebooks going back decades with everything from first pages to first chapters in it…
‘Tis the writer’s burden.