Stick to it? You've got to be kidding!!!!!!!!!! The next project picks me. And it doesn't wait until I've finished whatever I happen to be working on right now.
It sneaks into my dreams and won't let go until I start it. Absolutely hopeless to get a good night's sleep until I start it.
I start planning it in my head when I'm supposed to be going to sleep.
That's why I have so many WIPs.