“If you speak of the Devil, you will see his horns.” 16th-century Italian proverb (“Se parli del diavolo, vedrai le sue corna.” Cataplus, a mock Poem’, 1672 ).
This phrase appears in various Latin and Old English texts from the 16th century. The Italian writer Giovanni Torriano has the first recorded version in contemporary English, in Piazza Universale, 1666: “The English say, Talk of the Devil and he’s presently at your elbow.”
In the Christian world, it was seen as dangerous to speak about the Devil. There was by the clergy a prohibition to speak about the Devil or demons, like the prohibition on speaking the name of God. The numerous synonyms for the Devil – Old Nick, Prince of Darkness, the Horned One etc. are no doubt a consequence of this prohibition.
Maybe after reading this, you will see his horns. Let me know.