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will-o'-the-wisp - (noun) - 1: a light that appears at night over marshy ground; 2: a misleading or elusive goal or hope

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If you are near a swamp, the unidentified aerial phenomenon you see is probably not a UFO trying to abduct you, but a will-o'-the-wisp trying to lead you to your doom via drowning.  So cheer up and don't go towards the light.