>>> You get the (you think...) brilliant idea phase when you're all fired up, then you get "this is really boring" phase.
In my experience, there are 2 kinds of 'really boring' phase. One kind, as you mention it, is the less exciting part of the work, be it writing docs, or some edge case bugs, etc. The other kind is when you discover that you largely underestimated the complexity, or saw some major flaws in the initial idea. Like I've mentioned in my previous comment, maybe you start working on a game and find out some major flaws in the gameplay and can't see it being a fun game to play anymore. While it's not always obvious which case you are facing, in the later case, in my opinion, it's fine to halt the project. If you don't believe in it, nothing good will come out of it.
>>> It's not unusual to have problems with phase 1. But it's also the difference between being a professional and being a hobbyist.
I guess it depends on what's the purpose of the side projects. If it's something you try to make a business of (passive income kind of thing), then yeah you totally should get a bit of extra will power to get it shipped. But if it's something that is done just for fun, then I wouldn't sweat it that much.
Problem - I can't draw. I have no idea what I'm doing. I am completely terrified of making some kind of horrible messy fuck-up non-art and...
To keep it short - it's all fine. I'm not Durer, and I sketched something that didn't look much like rope. But it was way better than I expected.
The takeaway: there's a kind of pain barrier with a lot of projects. You think "This is not working, it's not going to work, I'm totally wasting my time on it", and all kinds of other critical thoughts.
Then you keep at it, and often - usually - it all works out.
The one exception I've found is that if projects for other people feel stuck, there's often a good external reason, and it's possible that you're genuinely wasting your time on them.
But if it's a solo project and it's not working, you don't have to force that iteration to work. But if you keep pushing and iterating and changing, something good falls out. IME the intense frustration is often the sign you're on the way to a breakthrough.