Excelling in virtually any profession at the top level almost requires you to believe that you are the best at what you do, or at least extremely good at it. That may be especially true in the field of athletics. And in football, a case can be made that the cornerback position above all demands it.
Cornerback is such a competitive position, in which you are always at a disadvantage, at least in this era of the game. Even the best tend to ‘lose’ half the time, in terms of allowing a reception. You have to have a short memory for your mistakes, and convince yourself that any big play you allow is a fluke.