Here's my experience. Until you have the luxury to pursue any side project you want, I found that side project that scratch your itch on your main job work best

Here's my experience. Until you have the luxury to pursue any side project you want, I found that side project that scratch your itch on your main job work best. You have fun with problem solving at your own pace, and also make your work life continuously a little better(because you know where your itch at, and since no one cares, so you do it yourself) At the end of the day, you ship something useful and practical and learn something new along the way. Ain't that count? Unless your side project = side business, now that'll be another beast. Even something you do out of love that doesn't involve money making, you still have to think about it, find time to do it and when you can't(mostly because your main job took all your time) you will feel guilty and depressed. And the cycle continue.... seriously, I think it's worse than having no side project.