blind alley vs mishap

blind alley

noun
  • Used other than figuratively or idiomatically: see blind, alley. A street or passageway that leads nowhere. 

  • A course of inquiry that leads nowhere. 

mishap

noun
  • Evil accident; ill luck; misfortune; mischance. 

  • An accident, mistake, or problem. 

How often have the words blind alley and mishap occurred in a corpus of books? (source: Google Ngram Viewer )