There are attributions to Gayle Sayers and Brian's Song, both around 1971. Nope, it is definitely not from either of those. The quote "I am third" was displayed prominently in the mess hall of a YMCA camp I attended (Camp Lackey, on Mt. San Jacinto near Palm Springs, CA) in 1965. Others say they were taught this concept in school in the 1950's. The concept is as old as Christianity, at least, so whoever put it into this simplest form is most likely lost ... oh well, whoever said it first probably doesn't care a lot about taking credit for it, right?