Ask HN: How do you ideate on a software idea?

I figured out everytime I have an idea that becomes too big to fit only inside my head, I start crazily taking notes on paper, on my phone, ecstatically following the pieces of features that come to my mind and trying not to forget everything. I soon jump on technical aspects, unveils new exciting opportunities to use X tech, Y algorithm or optimization. At some point, my white notebook is a maze of black arrows going in every directions, pointing to comments and squares, circles, and sometimes flowers. And then, it happens, I don't want to code it anymore, it looks solved but way too complex for me to handle. And I move to something else.

So I am thinking, how do you folks ideate on your side projects / work ideas? How do you keep it constrained to clear use cases without making it redundant or limiting? How do you start working on your ideas without losing the thrill?