Three reasons you may be falling behind in personal side-projects:
Fear of failing, masked behind over-analysis or the search for an impossible certainty of success. Specially if those projects are things you have not done before.
Trying to do too many things at once, which can be a form of hiding. If you want to get things done, you need to focus on the most important things every day.
Amateur mindset. There is no reason not to approach personal side-projects with the same professional mindset as any other project.
(Hat tip to my past-self.)