In what way does Mrs. Bucket try to prepare Charlie for possible disappointment regarding the presence of a golden ticket in his birthday candy bar?

As the family sits silently around Charlie and he prepares to open his birthday present of a bar of chocolate in order to see if he has located a golden ticket, Mrs. Bucket intervenes when she feels concerned about Charlie. She tells him gently that he should try not to be disappointed if his chocolate bar does not contain a golden ticket, since he "really can't expect to be as lucky as all that" (26).