diverge vs lose the thread

diverge

verb
  • To separate, to tend into a different direction (from another line or path). 

  • To become different; to run apart; to separate; to tend into different directions. 

  • To run apart; to separate; to tend into different directions. 

  • To become different, to separate (from another line or path). 

  • Not to converge: to have no limit, or no finite limit. 

  • Both stories start out the same way, but they diverge halfway through. 

lose the thread

verb
  • To get distracted and lose track of something (one's train of thought, a conversation). 

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