6. Greg Maddux
The first pitcher in major league history to win the Cy Young Award in four consecutive seasons, Maddux was a phenom during his prime. He won the World Series with the Atlanta Braves in 1995 and became a Hall of Famer in 2014. Due to his long list of accomplishments, you might be surprised his first season was terrible.
Maddux compiled a 6-14 record with a 5.61 ERA in his first full season with the Chicago Cubs in 1987. Nobody expected him to become an 18-time Gold Glove Award winner. Maddux also holds the record for most seasons finishing top 10 in the league in wins with 18.