let-down vs sadder and wiser

let-down

noun
  • A disappointment or anticlimax. 

  • The clearance of an aircraft to descend through clouds to clear air below, or the process of granting such a clearance. 

  • The neurohormonal release of milk in dairy cows or in breastfeeding human mothers. 

sadder and wiser

How often have the words let-down and sadder and wiser occurred in a corpus of books? (source: Google Ngram Viewer )