I built Dependabot (
https://dependabot.com), a service that checks your dependencies are up-to-date every morning and creates pull requests for you if they're not. Intention was to make dependency management suck less, whilst also adding a bit of runway to a bigger startup I wanted to do.
* Spent 2 months building it - much longer than I'd thought. The work required to get from a prototype (2 days) to a SaaS product (2 months) was way bigger that I'd thought. So much polish, and so many edge cases to consider when the client goes from "you" to "anyone else". Lesson: building something for other people takes a lot longer than building something for yourself.
* Tried to launch on Hacker News but failed to get any attention. Our blog post on "10 years of Rubysec data analysed" never made it off the "newest" page, despite being pretty solid content (spent two days building a Jupyter Notebook so anyone could replicate our results, etc.). Was a big psychological hit at the time. Lesson: there's lots of randomness in launches - don't rely on them to much.
* Thought GitHub Marketplace would list us and help with distribution, but it's been extremely hard to persuade them to. The jury is still out on this one, but they (understandably) want us to have lots of users before they invest in even assessing the app. Lesson: don't rely on the goodwill of third parties - unless you've got something they want/need, you'll be stumped if they decide they're not interested.
I haven't given up yet, and I still really believe in the product, but it's been a much harder journey than expected! Marketing has been by far the toughest part, and I don't have a solution to it yet.