Superstition is a big part of the psychology of baseball. And I think it helps players to improve their concentration.
Superstition is basically just an arbitrary routine. You do the same thing over and over again because you believe, for no verifiable reason, that it helps your performance. This feeling of comfort and familiarity can help a player to block out the outside world and concentrate only on the game. It gives them a feeling of safety and security that is very calming.