silliness vs thoughtlessness

silliness

noun
  • That which is perceived as silly or frivolous. 

  • An act that is silly; a result of being silly. 

thoughtlessness

noun
  • heedless disregard for the consequences of one's actions 

  • disregard for other's feelings 

How often have the words silliness and thoughtlessness occurred in a corpus of books? (source: Google Ngram Viewer )