I'll start - had the usual example today. Started cutting a garnet last night and spent a couple of hours perfecting the pavilion (PCP design so I complete the facets, including polishing) just 'tweaking up' the girdle polish and must have pressed a tiny bit too hard and the stone heads west. Only a small stone and obviously re-dopped to be even smaller.
Don't you hate the waste of time and effort when this happens?