I noticed a pattern with many of my side-projects: I would work furiously in my spare time for a few months, and wind up with something "very nearly done". Then I'd take a break for a week or two, just to get some perspective and figure out what really needed to be done to "finish" the project.

Of course I never returned to any of these projects.

My new approach is just to do something on my current side project, without fail, every day. There is no "finish", there's just work, and it really is more enjoyable.