Ask HN: How do you deal with abandoning a project?

I'm sure every developer has many side-projects and work projects they have spend huge amounts of time on, only to abandon for a variety of reasons. Maybe a competing project was better resourced, or the community shifted to the latest shiny thing, or maybe a decision to kill a project came down from higher ups.

When I think about the time I have poured into such projects it makes me feel like I have wasted my life. Sure there are lessons learned and experience gained, but if I could go back in time I would tell myself to never get involved in the first place.

For work projects you are making money in exchange for your services, but going unnecessarily above-and-beyond and working long hours, or spending time on weekends on side-projects and open-source that you later abandon just seems like a huge waste of time.

It never really causes complete burn-out though, it just makes me a little more cautious about diving into new projects as I get older and makes me more inclined think about the opportunity cost. But what if my greatest contributions are still yet to come and my cautiousness will prevent me from exploring them.

I usually rationalize it to myself as: you enjoyed working on it at the time, and you learned a lot.

I wonder how other people deal with the thought of having poured so much time into a project only to abandon it?