I know that I have to unsew because I have a standard of perfection (that does not necessarily mean absolutely perfect). I know that if I start out not having things right that the problem grows because making a quilt is a building process. If the beginning steps are sloppy it doesn't just make itself right. I really try to minimize it by measuring carefully and not trying shortcuts that could lead to big problems. If I chain piece I verify that I have it put together correctly before making a gazillion. Make test blocks before making 30. But no matter how careful I think I am, I still have some unsewing to do. It is just part of the process. I like the comment above, we have erasers and delete buttons.