What focuses me is remembering this mantra attributed to Steve Jobs:

Real Artists Ship

The idea that nothing you’re working on is real until you ship it to customers, users, or whoever the stakeholders are.

Helps a lot against bouncing between lots of projects and not making much progress on any of them.

I've learned that when working on a new project, having a few friends using it (via TestFlight if it's Mac/iOS) incentivizes me very well to keep going. And they're happy if they text me about a bug and it's fixed in a few hours! It seems like a positive feedback loop.