will-o'-the-wisp

will-o'-the-wisp (unobtainable, unreachable, romantic dream or hope; hazy, nebulous, phantom pursuit; anything that deludes or misleads by luring on) — нечто обманчивое, неуловимое, призрачное, иллюзорное; обманчивая надежда; недостижимая, иллюзорная мечта

.....Romantic will-o’-the-wisp phantasms of perfect eternal love and unending marital bliss belong in the novels of the eighteenth century.
.....Stop following your will-o’-the-wisp dreams and imaginary fantasies and come down to earth and take a good, hard, long look at reality.
.....The Legend of Sleepy Hollow is the product of a will-o’-the-wisp phantom pursuit based on early American heritage.
.....Excessive higher dependence on foreign capital inflows and a rise in exports is likely to be dangerous. Unless there is a sustained growth in exports arising from improvement in the competitive strength of the Indian industry, our hope to recover will be the will-o'-the-wisp .

Origin:

The will-o'-the-wisp /ˌwɪl ə ðə ˈwɪsp/ or ignis fatuus (/ˌɪɡnɨs ˈfætʃuːəs/; Medieval Latin: "foolish fire"), also known as will-o'-wisp , is sometimes called jack-o'-lantern, "spooklights," or "ghost lights" are atmospheric ghost lights seen by travellers at night, especially over bogs, swamps or marshes. It resembles a flickering lamp and is said to recede if approached, drawing travellers from the safe paths.
(призрачные огни, бродячие огни, блуждающие огоньки и пр).