Friday's sail, sure to fail.

The saying expresses a traditional seafaring superstition that beginning a voyage on a Friday brings bad luck and makes failure likely. Its compact rhyme makes the warning memorable, not reliable guidance about travel or success.

It can also be used figuratively to label a badly timed or ill-omened start. In that use, it alludes to traditional beliefs about unlucky departures rather than making a factual forecast.

Use it when discussing nautical folklore or jokingly cautioning against starting a plan on a Friday. It has an archaic or playful proverbial tone and may sound superstitious if presented as serious advice.