One who fears the unknown will one day take fright in his own backside

Vizier:

Lemuria? Sinbad:
Aye, a mythical island. Mariners have been searching for it for centuries. Rachid:
They say it is all that is left of a once-mighty continent, now sunk beneath the waves, a place of untold dangers and death. Sinbad:
One who fears the unknown will one day take fright in his own backside