The song was written specifically for Doris Day, who starred in the film and performed the song in it. The song's theme of fate and acceptance was intended to reflect the film's plot and Doris Day's character in the film.
It's worth noting that the phrase "Que Sera, Sera" is a Spanish proverb, meaning "What will be, will be". The song uses the Spanish phrase as its title and recurring refrain, creating a sense of optimism and acceptance in the face of uncertainty.
The song's popularity went far beyond the film and became a global hit, achieving iconic status in popular culture.