The magic key for me is to tell no one about my project, until it's in a workable state. Just telling someone what I want to do, including the details of my plans, is sometimes enough for me to never actually start with it. But keeping it quiet—which is very hard mind you—leads to me actually acting on my plans.
I learned this about myself as well, after always hearing advice to share with others so you're accountable. I don't always want others "checking in" on my progress.
Same.
Maybe it's just a fear of commitment or perfectionism?
Because as soon as one of those materials gets used it often can't be undone and the project most likely will no longer be as perfect as the idea.