The joke around here is that I technically only need ONE ball of yarn (I'm a knitter), because I could just rip out a half-finished project and start on a new one using the same ball of yarn over and over. This way my knitting wouldn't take up an entire closet.
My neatnik DH who hates clutter is especially fond of this innovative notion, for whatever it's worth.
I
do finish most of my projects. But sometimes I will drop one for months or even years before picking it up again and working on it. I just seem to lose the driving force behind the motivation, and the project no longer fuels anything for me personally. It isn't that I can't stay focused on it. I just choose to move on to something else because it is no longer challenging or novel enough to be interesting. I suppose that I feel that my hobbies and interests shouldn't feel like drudgery.