The line comes from Forrest Gump, the 1994 film directed by Robert Zemeckis and starring Tom Hanks in the title role. Forrest says it to Jenny while explaining that even though he may not be smart, he knows what love is. The film was a major cultural hit and won the Academy Award for Best Picture, which helped its dialogue enter everyday language. Decades later the quote is clipped and reused as a reaction sound for moments of honest confusion or humility.