the one-eyed stag (misfortune often comes from where you least expect it)

stag, blind in one eye, always grazed by the sea, so that he could keep a look out for approaching hounds, believing this to be the only threat. He never bothered to turn his good eye to the sea, so when sailors from a ship came ashore he never noticed them, until he was shot with their arrow, fatally wounding him.