In the Romance of the Three Kingdoms, Emperor Xian, attacked by the generals Li Jue and Guo Si, is advised to summon Cao Cao. Before the messenger can even reach him, Cao Cao's officer Xiahou Dun arrives to save the emperor, the warlord had already moved. From the scene came the saying shuo Cao Cao, Cao Cao dao: mention Cao Cao and Cao Cao arrives, used exactly like speak of the devil when someone appears mid-conversation.
The novel casts Cao Cao as its great villain, the ruthless genius, so he slides neatly into the devil slot of the English idiom. But the story underneath the idiom is not menace; it is logistics. He arrives because he was already coming. The saying preserves a management compliment inside a devil formula: the person who shows up before being summoned runs the empire, or rescues it, whichever came first.
The claim: both versions of the idiom encode the old superstition that attention is invocation, naming a thing bends it toward you, and Cao Cao's version adds the modern twist: the powerful arrive when mentioned because they are listening, the warlord as notification system. Verdict: naming-summons is documented folk belief worldwide, and the listening-power reading writes itself in the age of triggered alerts. Speak of the algorithm, and it is already in the room. Cao Cao would have approved of push notifications.
Why does the idiom reward the man who arrives before he is asked?