I have recently finished my 'end of two year course' quilt assessment - a 5' square bed topper, appliquéd, quilted, bordered etc. We have to add a 'hanging sleeve' across the top so that they can be hung up for their display at a quilt show. I carefully and beautifully hand stitched mine, really level, pleased with myself.
However:
On turning the quilt over I had managed to stitch the wretched sleeve to the side and not to the top...........
Much swearing and unpicking........and not very good sewing it back on, with a caveat that it is for temporary use only as it needs to go on a bed!
Pillock.