let go vs retain

let go

verb
  • To release from one's grasp; to go from a state of holding on to a state of no longer holding on. 

  • To dismiss from employment. 

  • To ignore (a comment, etc.). 

  • To emotionally disengage or to distract oneself from a situation. 

  • To fail to maintain a standard of appearance, behavior, or performance. 

  • Used other than figuratively or idiomatically: see let, go. 

  • To gain weight 

retain

verb
  • To hold back (a pupil) instead of allowing them to advance to the next class or year. 

  • To employ by paying a retainer. 

  • To keep in one's pay or service. 

  • To keep in possession or use. 

  • To hold secure. 

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