This quote comes from Whitebeard in One Piece during the Marineford arc, where he declares that the One Piece is real. The line became a meme far beyond anime spaces because its delivery is so absolute and dramatic. It spread through reaction edits, ironic captions and short-form videos that frame small discoveries like world-changing revelations. It still gets reused because even people who have not watched the series recognize the line as a perfect overblown confirmation.