"If we're going to win the pennant, we've got to start thinking we're not as good as we think we are"

In this quote, Casey Stengel is stressing the significance of humility and self-awareness in attaining success. He is suggesting that in order to truly reach our full capacity and win the pennant (a sign of victory in baseball), we need to release our egos and acknowledge that we may not be as great as we believe ourselves to be. By acknowledging our weaknesses and areas for improvement, we can work towards progressing and eventually accomplish our objectives. Stengel's words work as a suggestion to stay grounded and constantly pursue development, rather than ending up being contented in our perceived abilities.