Ah, the "9 plus 10 is 21" meme originates from a Vine video that went viral. The video features a young boy being asked what's 9 plus 10, to which he confidently responds with "21." The funny nature of his incorrect answer, coupled with his unshakeable conviction, caught the internet's attention and turned it into a popular meme. Memes have an uncanny ability to spread and take on a life of their own in the vast realm of online culture. It just goes to show how humor can unite us all!