Hang by a thread

In a precarious, fragile state, teetering on the edge of collapse or survival, held by the slimmest chance.

From ancient Greece, tied to the Sword of Damocles; a tale from Cicero (45 BCE) where a blade hung by a horsehair over a flatterer, symbolizing peril. English adapted it by the 16th century, as in a 1530s text on a 'thread-hung' fate. By the 19th century, it was common, as in Dickens' 1841 'Barnaby Rudge,' reflecting a love of classical dread and Victorian suspense, woven into a stark idiom of fragility.