I have the opposite issue. I can't bring myself to start another before the one I am working on is done. I know this comes from my upbringing. When I would even start to think about making anything new... my Mom would ask "did you finish the one you are working on?"... We had a very strict rule no new fabric could be cut till the the current project was done. There was another rule.. fabric had to be .50 cents a yard or less. Patterns had to have at least 3 different items( skirt , pants, and something else).. and those had to be under. 50 cents.
So even though I have tried to start a project without completing one... it just creates stress.. this overwhelming feeling that what I am doing is wrong. Funny how we can get conditoned and it stays with us for a lifetime.