ax to grind vs unhappiness

ax to grind

noun
  • A grudge or grievance, with implications of confrontation. 

  • A proposition or point of view to advocate, especially motivated by self-interest. 

unhappiness

noun
  • The feeling of not being happy 

How often have the words ax to grind and unhappiness occurred in a corpus of books? (source: Google Ngram Viewer )