comfortable in one's own skin vs self-assertive

comfortable in one's own skin

adj
  • Relaxed and confident in one's manner of presenting oneself and interacting with others; conveying the impression that one has a clear, satisfying understanding of one's own abilities and situation. 

self-assertive

adj
  • determined to advance one's own personality or views 

How often have the words comfortable in one's own skin and self-assertive occurred in a corpus of books? (source: Google Ngram Viewer )