You can improve matters by a) scoping projects less ambitiously and b) enforcing a novelty budget on yourself.

A very ambitious project which you will never finish might actually be three small projects which you will finish and seventeen small follow-up projects you'll decide to never take on. Better to get the three under your belt than try to sprint in 20 directions at once and bail with nothing to show for it.

Say that you decide "I'm going to write a personal ontology engine flexible enough to store everything I know, with a snazzy, super intuitive frontend written in <new-to-me framework X>, a plug-in system for easily creating visualizations for specific types of data (oh, like, what if my personal knowledge DB could take FEN+PGN and let me replay and annotate interesting chess games in-line, that'd be so sweet!), a bespoke query language, the whole thing will be backed by <new-to-me storage backend Y> and, hell, I've been meaning to start containerizing apps at work, I wonder if I should be using docker-compose as I do this or maybe like kubectl, ...also I need to dive into the literature around building ontologies, knowledge graphs, etc. Also, it should probably have emacs keybindings. Probably also support for rebinding keys and defining macros too. Also, it should have a pluggable module interface for scraping semi-structured data sources containing things I don't actually know right now but which I would like to learn at some point. Maybe I can use the hyperlink structure of Wikipedia documents as a scaffold to get the thing started. Oh geez, this is really going to need to support multimedia as well, not just text. Really, this kind of thing would be very valuable in many different contexts. It'd be great if it could be used to automatically generate questions about a topic. I could integrate a spaced repetition algorithm with the question generating bit and then I'd have an amazing study tool. Hmmm, I'd better keep the whole thing as flexible as possible so maybe at some point down the road I can productize it! Sure it's a long shot, but it'd be revolutionary if I could pull it off. I'll start tonight!

To steal from Alan Perlis, "When someone says 'I want to build a personal knowledge DB as a side project and I want it to have perfect ergonomics, top grade discoverability, unlimited extensibility, and unparalleled ease of use,' give him a lollipop."

Even if you don't get stuck in feature daydreams or analysis paralysis and manage to start the thing, your "gee it'd be swell if" side project has a five or ten plus year "labor of love" todo list attached to it. The mismatch will sink you unless against all odds this actually is your labor of love.

As a personal example of the scoping into smaller projects which were standalone (though not a good example of enforcing a novelty budget) I wanted to make a personal activity tracker in 2018 or so. Initial conception was the all-singing, all-dancing, kitchen sink Swiss Army knife of personal data tracking and visualization, implemented in all the technologies I'd been meaning to try out. The backend would be a gleaming beacon of modern infrastructure with everything containerized from the outset, code written in Rust (in which I was a neophyte), phone app written in Kotlin (in which I'd only done the Koans, and with no other mobile dev background, but hey, "Anko" seems to be The Thing to use now, hmm)...

Having been bitten by the bug you ask about in the past, I set that aside. Instead, I did a bunch of smaller projects with each on their own bringing a reasonable sense of completion:

1. Two Python scripts - one to configure desktop OS notifications to fire on a cron schedule ("Nag! Update your data for <x>") and one for CRUD operations on time series metadata and data points themselves. Just backed by local sqlite. Finished in <1 day. Hey look, MVP! Time to start tracking data!

2. Docker setup for building a Rust binary and then trimming away build tooling to get a deployable artifact. 1-2 days? Containerization itch: scratched. Could be a 101 level blog post.

3. PostgreSQL docker image with CREATE/DROP TABLE scripts. Half a day? I guess I learned about Docker data volumes. I can refer back to this Dockerfile in the future, which is like 9/10ths of how I make progress quickly on new projects.

4. docker-compose setup for a Hello World level Rust binary that reads a record from a postgres db running in a separate container and writes it to stdout. Half a day? Hooray, orchestration.

5. "Hello World"-as-a-Service web app that uses Rocket to send a Hello World application/text response. Not very long to finish. Novelty framework itch, scratched.

6. Learn about Diesel. Use Diesel to make a single SELECT COUNT(*) query against the DB. Send query result as application/text response on a dummy endpoint. Done. Could probably be broken off into a "Intro to X with Y and Z" type blog post.

7. Update SELECT-as-a-Service web app to make a meatier query and serialize response to JSON. Learn about Rocket request guards for managing DB connections. Another day or two? If step six wasn't enough for a 101 level blog post on the topic, seven definitely is.

8. Port the Python CRUD functionality to a Rust REST API atop Postgres. Deliverable: approximately all the backend we'll need.

9. Update the Python CLI to use the REST endpoints. Another day? Done.

10. Start doing Android Hello World apps. Using unfamiliar APIs in an unfamiliar dev environment in an unfamiliar (but nice!) language. Eww, this sucks. I'm not having fun any more. Maybe I should first learn vanilla Java Android app development, then Kotlin, then build on that basis with Anko, then...

And then, at that point, I realized that aside from enjoying daydreaming about the idea of a personal activity tracker, I didn't actually give a crap about having an all-singing, all-dancing personal activity tracker. While I'd been happily chugging along building the thing, I didn't care enough about the underlying functionality to bother taking two minutes a day to, y'know, actually track the data when the MVP nag script ran on its cron. When I bailed though, instead of "ugh, another incomplete useless waste of time," I ended up with several completed small projects and more knowledge about what I actually wanted (to futz around building a personal activity tracker, not to have one).