Never finish what I start and terrible procrastinator?

Can someone please tell me why I never seem to be able to finish what I start, I put stuff off until it can't be put off anymore. It's not that I'm lazy, if i'm given a task i'll work my off to get it done and get it done right, but when it comes to doing things on my own, i start, but never finish. I love to sew and crochet/knit, i'll start like 5 different things on the same day then get overwhelmed and just say screw it. Why?