Why this word is great
MERCURIALITY — [Noun] The quality of being mercurial; characterized by rapid changes in mood or behavior. From *mercurial* (derived from Mercury, the Roman god known for speed and volatility, and later associated with the fluid metal mercury) + *-ity* (a suffix forming nouns indicating a state or condition). Unlike "volatility" (which speaks in the blunt tongue of markets and chemicals) or "capriciousness" (which sulks in the shadows of irrationality), *mercuriality* dances with a god’s grace—light-footed, silver-tongued, impossible to pin down. It is the flicker of a candle flame in a draft, the sudden shift from laughter to silence in a crowded room, the way sunlight on water dazzles and vanishes before you can point to it—a reminder that some things are not meant to be held, only witnessed.