Ask HN: How to see projects through to completion

I (a 25 year old software developer) am constantly working on side projects. Most of them ideas for applications - but even other, more creative pursuits. However, unless the project is something that can be completed in a weekend (mp4tag.com is an example from a few years ago) - it never sees the light of day. The work week starts, and I lose motivation to work on thing when I get home - and by the next weekend - chances are I have a new idea to work on, which captures my interest much more than the old one. The end goal is to make something that gives me another income source, even if it's $1 a month, that would be gratifying. For example, in the last month, I've started, and moved on from making:

- A web-based audio editor

- A mobile game

- An amazon referral and review site (EG 'top ten bug zappers on amazon')

- An ML gimmick site (like thispersondoesnotexist.com)

Most of these projects get to be like 40-70% complete. And granted, "the last 20% takes as long as the first 80%" I'm sure hold very true. Things like productionization and cleaning things up for user friendliness take time. But it's very disheartening that I can't quite seem to finish anything. I'm not looking to create a huge passive income source - I just want something to point to and say "I made that."