The story
From cliff + hanger, evoking the image of someone left hanging from a cliff, thereby having an uncertain fate. The term cliffhanger is considered to have originated with the serialized version of Thomas Hardy's A Pair of Blue Eyes, published in Tinsley's Magazine in the 1870s, in which the character Henry Knight is left hanging off of a cliff. It was inspired by a real life story from his wife Emma's childhood, when she had to rescue one of her school friends from a similar position.
Etymology from Wiktionary, CC BY-SA 4.0.