自zì言yán自zì语yǔ

Literal: oneself speaks, oneself talks
Figurative: To talk to oneself, muttering quietly without addressing anyone in particular.

Where does 自言自语 come from?

It does not come from a particular tale; it is a set phrase with a parallel structure, repeating 自 ("oneself") before two near-synonymous verbs for speaking, 言 and 语, to stress that one is both speaker and listener. It already appears in Ming-era vernacular prose and remains very common today, both in speech and in narration.

How is 自言自语 used? Two examples

他tā一yī个ge人rén坐zuò在zài角jiǎo落luò里lǐ自zì言yán自zì语yǔ，谁shéi也yě听tīng不bù清qīng他tā在zài说shuō什shén么me。
He sat alone in the corner talking to himself, and no one could make out what he was saying.
奶nǎi奶nai一yī边biān做zuò饭fàn一yī边biān自zì言yán自zì语yǔ，好hǎo像xiàng在zài跟gēn谁shéi聊liáo天tiān。
Grandma cooked while muttering to herself, as if she were chatting with someone.

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