You can work on a lot of different problems and still do the creative garden cultivation that the previous poster said. I do that. I've got about 10 prototypes

You can work on a lot of different problems and still do the creative garden cultivation that the previous poster said. I do that. I've got about 10 prototypes for board and card games actively going at once at the moment, and I write down fresh ideas that pop into my head to come back to later. Even if months pass, I'll get spontaneous ideas to certain projects that improve them a ton. But I have to feed my brain with fuel for inspiration constantly, and actively try to apply any interesting idea to my existing projects and see if they inspire anything new for them. I can't find the quote now (It's written in a notebook I don't have on me at the moment), but this is apparently how Richard Feynman approached work, although by working on multiple problems at once, not projects (although all of my projects have problems :).