The clip comes from a short Vine video that spread widely in the mid 2010s, built around a child being asked what nine plus ten equals. His answer of twenty one became a standalone catchphrase, remixed into edits, remakes and reaction videos far beyond the original post. The phrase was repeated, quoted in classrooms and turned into a shorthand for confidently wrong answers. It remains popular because the joke needs no setup, anyone hearing the numbers instantly understands why the response is funny.