hesitant vs unflappable

hesitant

adj
  • Tending to hesitate, wait, or proceed with caution or reservation. 

unflappable

adj
  • Remaining composed and level-headed at all times; impossible to fluster; not becoming frustrated or irritated easily. 

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