Authors:

When you've learned to believe in yourself, there's no telling how good a player you can be. That's because you have the mental edge.

Rod Carew, Frank Pace, Armen Keteyian, Joe Mauer (2012). “Rod Carew's Hit to Win: Batting Tips and Techniques from a Baseball Hall of Famer”, p.88, MVP Books
When you've learned to believe in yourself, there's no telling how good a player you can be. That's because you have the mental edge.