The phrase comes from Game of Thrones, the HBO fantasy drama based on George R. R. Martin's novels, where older characters use it for young people who have only known easy times. Summer children in that world have never lived through a long winter, so the line implies innocence about hardship ahead. After the show became a global hit, viewers lifted the quote into reaction videos, memes and social posts whenever someone sounded blissfully unaware. It endures because it packs sympathy, superiority and foreshadowing into five gentle words.