IMO building a side project with the goal that it will take off (and to hopefully get rich) is not the right motivation. Spoiler: it probably won't take off and you probably won't get rich. Minor survivorship bias.

Work on a side project because it's interesting (e.g. you want to learn the tech) or because it's useful to you (i.e. you want to use it). Not because it may make you rich.

In the former case, you may lose interest, but that's okay: you've learned in the process. In the latter, if you get to a point where you can use it, it's really rewarding.

My most successful side project to date is one that has “always-free, no-ads” as a motto, so it will always be a money sink.

Sometimes I spend a week refactoring core stuff, sometimes it stays forgotten for months on end. I still come back to it when I want to test some ideas, mostly because it has a decent chunk of data to feel I’m “solving problems at scale”.