Building your own thing is great, but one unintended consequence is that if your thing actually becomes popular, you'll be expected to maintain it forever. If your interests or preferred tech stack change, you are stuck with a mountain of your own tech debt. Chances are no one will ever rescue you.

For juniors who barely even know that their own preferences are, much less their long term career goals, this can be a serious downside.

When I was just starting, I had a side project that got reasonably popular but I never expected to be maintaining it years later, and it became a serious mental burden. I think the author is correct that you know you're doing it right when it feels like a chore, but it is kind of a bummer if a junior gets sucked into this maintenance burden without understanding the consequences. As a more senior developer, I think long and hard before seriously committing to a new open source project, and ask myself if I want to be maintaining it in several years before I write a line of code.