My worst mistake was on the first and only "trip around the world" quilt I've ever made. After it was sewn all together I was doing simple straight line quilting through the darkest blocks. Then through the next darkest blocks. No problem. But when I got to the 2 sets of light blocks, they didn't line up into a diamond, they were a rectangle???? Turns out I had set one entire quarter piece of the quilt in sideways--but because of the darker fabric it looked OK until you looked at the light fabric. Sigh. This was to be a gift for a friend and I decided there was no way I was going to rip it all apart. So I called it a "puzzle" quilt and gave it to my friend anyway. They loved it, and I love telling the story.