Let’s be clear up front about something: Just being on GitHub in a public repo does not make your code open source. Copyright in nearly all countries attaches automatically when a work is fixed in a medium, without need for any action by the author. For any code that has not been licensed by the author, it is only the author who can exercise the rights associated with copyright ownership. Unlicensed code—no matter how publicly accessible—is a ticking time bomb for anyone who is unwise enough to use it.
Unlicensed code is unsafe code, period.
When you write open source code, you know that it not only has to work, it has to work in situations you never dreamed of and may not have planned for. Maybe you only had one very narrow use case for your code and invoked it in exactly the same way every time.
The true heart of open source isn’t the code at all: it’s the community.
announce that you’re thinking of creating a new project. Talk about your design goals and how you plan to achieve them. Request input, listen to similar (but maybe not identical) use cases, and build that information into your process as you write code.
This process doesn’t end with the initial announcement. If you want your project to be adopted and used by other people, you need to develop it that way too. This isn’t a barrier to entry; it’s just a pattern to use.
Open source work sharpens your skills in ways you never realized were dull—from writing cleaner, more maintainable code to learning how to communicate well and work as a team.