Usually I tell people they are welcome to shop my UFO stack and that eventually it will get finished, just don't hold your breath! - while pointing to ones that are a few steps farther along that are already claimed and were supposed to be for xxxxx birthday two years ago or whatever.
I do what I do because I want to do it. I may put a project aside because I'm not happy with how it's coming along. Sometimes working on something else will help clear up my thinking on the original project so I can go back and finish it or at least make progress. This is the main reason I don't like doing something major with a strict timeline. Then I feel like I can't put it aside even if I'm getting frustrated with some part of the process. Takes the fun out.