baptism of fire vs unpleasant experience

baptism of fire

noun
  • Martyrdom by immolation. 

  • Tribulation endured as spiritual discipline. 

  • The gift of the Holy Spirit. 

  • The first experience of a severe ordeal, especially a first experience of military combat 

unpleasant experience

How often have the words baptism of fire and unpleasant experience occurred in a corpus of books? (source: Google Ngram Viewer )