1 or 2. I really try hard, and I make many mistakes, but I've learned the seam ripper is my friend, and a part of sewing. I enjoy the process much more that way. It's not the end of the world if I make a mistake I can't fix, but I try to be well organized and really think about what I'm doing so it turns out well. THe mistakes do become "design choices" at times.
I agree with so many on the pet-peeves thread -- I make the most mistakes when I'm not concentrating!