nonchalance vs self-confidence

nonchalance

noun
  • Indifference, unconcern; carelessness; coolness; disregard, detachment. 

self-confidence

noun
  • The state of being self-confident 

  • A measure of one's belief in one's own abilities 

How often have the words nonchalance and self-confidence occurred in a corpus of books? (source: Google Ngram Viewer )