The line comes from The Lord of the Rings: The Fellowship of the Ring, released in 2001, where Ian McKellen as Gandalf faces the Balrog in the Mines of Moria. In the scene Gandalf first declares that the creature cannot pass, then delivers the stronger You shall not pass as he drives his staff into the bridge. Clips and quotes spread widely online during the early meme era, and the phrase became shorthand for any stubborn refusal. Its mix of fantasy gravitas and everyday blocking situations keeps it in constant reuse.