I just assign myself to work on it for one hour every day (or every other day). Then it gets done. It might get done later than originally planned, but it won't be undone forever. This is different from a part that is simply too hard - I leave it for a bit and step back to see if there is another way of doing it. Yes, I've taken out huge parts of a quilt that wasn't working and redone them. That is why I make sure to use a large stitch.
