lost soul vs sad sack

lost soul

noun
  • One who is forlorn, who lacks direction, purpose, or motivation in life. 

  • A soul that is destined to go to hell; a person possessing such a soul. 

sad sack

noun
  • An incompetent or inept person. 

  • A perennial failure or victim of misfortune. 

How often have the words lost soul and sad sack occurred in a corpus of books? (source: Google Ngram Viewer )