He was all at sea when he began his new job. What does the idiom/phrase "at sea" mean?

He was all at sea when he began his new job. What does the idiom/phrase "at sea" mean?

Explanation
  • The idiom "at sea" means being confused, puzzled, or unsure about what to do.
  • It originates from the feeling of being lost or directionless while on a vast ocean.