How about cutting an arrow shelf in on the wrong side ,making a southpaw when I wanted a rightie.
How about nearly completing an osage bow ,then realizing there were 2 different growth rings on the back.
How about finishing the tiller on a nice elm flatbow,then,(before gluing on tip overlays),stretching its new string out and splitting the end of the limb 5" deep.
I'm sure if I thought about it,I could come up with some more. God Bless