will-o'-the-wisp

/W IH1 L OW0 DH AH0 W IH0 S P/
noun
  1. 1

    A strange light that attracts travellers from pathways into dangerous marshes or graveyards.

  2. 2

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

Source: https://en.wiktionary.org/wiki/will%20o'%20the%20wisp, https://en.wiktionary.org/wiki/will-o'-the-wisp