> Also it can give a feeling that it was not a waste of time
Another way to avoid that feeling is changing your mindset around what's "abandoned" vs "completed". "Completed" doesn't have to mean "published project and made it FOSS" or whatever, it could literally be "Scratched an itch to play around with library X's APIs" or something, or just "Wanted to see if it was possible".
Nowdays I "complete" every single of my side-projects, some of them in some hours, because "completed" no longer has to mean "it's public and people can use it", mentally this feels a lot better :)