will o' the wisp
n//ˌwɪləðəˈwɪsp//irrbloss, lyktgubbe, bländverk
(British, _, folklore) 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.
(figurative) A delusionary or otherwise unachievable goal that one feels compelled to pursue.