delusion vs will o' the wisp

delusion

noun
  • The state of being deluded or misled, or process of deluding somebody. 

  • A false belief that is resistant to confrontation with actual facts. 

  • A fixed, false belief, that will not change, despite evidence to the contrary. 

  • That which is falsely or delusively believed or propagated; false belief; error in belief. 

will o' the wisp

noun
  • A delusionary or otherwise unachievable goal that one feels compelled to pursue. 

  • A flickering light or lantern, especially over bogs, swamps or marshes, held by a supernatural creature who uses it to lure travelers at night to their demise. 

How often have the words delusion and will o' the wisp occurred in a corpus of books? (source: Google Ngram Viewer )