Dr. Seuss Wrote His Most Famous Book On A Bet

American author and illustrator Dr. Seuss (Theodor Seuss Geisel, 1904 - 1991), works on illustrations for one of his children's books at his desk at home in La Jolla, California, April 1957. Photo by Gene Lester / Getty Images

Nowadays, world-famous children's author Dr. Seuss is one of the most well-known writers on the planet. "Green Eggs and Ham", one of his most successful books, sold over 8 million copies by 2016 -- but would you believe he wrote it based entirely on a bet?