Caveat: 열길 물 속은 알아도 한 길 사람 속은 모른다

열   길       물     속은   알아도    
ten gil [of] water inside know-BUT
한       길                         사람          속은          모른다
one gil [of] a person inside don’t-know
One can know ten gil of water,
but one can’t know even one gil of a person.
A “gil” is a traditional measure, maybe 10 or 11 feet, but used as a “fathom” in English.
People are unfathomable. Um. Yeah.