This sounds cliche and obvious, but it made a big difference for me:
I found myself dreaming of shipping a project, or writing a book - whatever. But, then I would stay in the dream or possibility of what could happen if I did those things - but I wasn't actually doing enough to make them happen.
So, I sat down on a Saturday morning, and wrote down what I would feel "unfulfilled" with in life if I didn't try them. Then, I wrote down a tangible plan to try them. It will takes years, but I will give them a go.
I found that for me, it was the "what if" that was killing me, so I am eliminating that element and will let the chips fall where they may.