will o' the wisp

will-o'-the-wisp

1. A unrealistic, unattainable, or delusional hope or goal. The mobile phone market has proven a will-o'-the-wisp for the giant tech company, despite the huge amount of resources they've poured into staking their claim in it. As we've seen time and time again, attempting to change or repeal the amendment will forever be a will-o'-the-wisp.
2. A person or thing that is or seems to be fleeting, intangible, or illusory. The president's stance on the issue has been something of a will-o'-the wisp, seeming to change or disappear entirely as the political climate dictates. The linebacker has been a will-o'-the-wisp all evening, appearing seemingly out of nowhere to deliver bone-rattling tackles.
Farlex Dictionary of Idioms.

will o' the wisp

An unattainable goal. Will o' the wisp is one of the names of the marsh gas phenomenon that causes lights suddenly to appear and disappear over swampy ground (ignis fatuus is another term). Trying to catch a will o' the wisp is impossible, much like trying to catch lightning in a bottle, and so the phrase came to mean anything that can't be done.
See also: will, wisp
Endangered Phrases by Steven D. Price
See also:
  • will-o'-the-wisp
  • wisp
  • want (one's) head examined
  • need (one's) head tested
  • need your head examined
  • need, want, etc. your head examined
  • need (one's) head examined
  • be in a dream world
  • be living in a fool's paradise
  • live in a fool's paradise