The two main things that have kept me motivated through large side projects, even when burnout has set in: - Building something that I really want. For example

The two main things that have kept me motivated through large side projects, even when burnout has set in: - Building something that I really want. For example, the project I've been working on for the past few months is something that's been brewing in my head for several years. - Sharing the fruits of my labor. At the end of my last large project, I got the satisfaction of knowing the product would get regular public use. In my current project, I've been open sourcing components as I've progressed, so even though it will be months before the project's complete, I have had some milestones of satisfaction. If the end result is something you can sell or profit from, that is a huge motivator as well, although I think my first point about building something you're really passionate about is more important.