Puzzled, perplexed, completely confused (about a subject or some task at hand), lost, bewildered. This idiom transfers the condition of a vessel that has lost its bearings to the human mind. Charles Dickens used it in Little Dorrit (1855):
I tried to do well in this class, but I've been at sea since we started.
When it comes to higher math, John is totally at sea.
When it comes to higher math, John is totally at sea.
by Nalaar September 09, 2017