hold the line vs stick to

hold the line

verb
  • To firmly maintain one's viewpoint, principles, or situation; to refuse to change one's practices or plans. 

stick to

verb
  • To persist; to continue (to use, do, etc.) 

  • Used other than figuratively or idiomatically: see stick, to. 

How often have the words hold the line and stick to occurred in a corpus of books? (source: Google Ngram Viewer )