let go vs shut down

let go

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

  • To dismiss from employment. 

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

  • To ignore (a comment, etc.). 

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

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

  • To gain weight 

shut down

verb
  • To emotionally withdraw into oneself as a defense mechanism; to block out external stressors. 

  • To pass (another vehicle), especially quickly. 

  • To close, terminate, or end. 

  • To turn off or stop. 

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