Fixing something wrong

          If there's something
          wrong with the third
          act,   it's   really
          in  the  first  act.

This quote from Billy Wilder, Austrian-born writer and film-director (1906-2002), reminds me of a similar observation I have made about my mathematical work -- when a reviewer notes a problem near the end, usually the fix is near the beginning.          And so it goes . . .