Why, while walking home, does Wang Lung yell that his child is a girl in The Good Earth?
Girl children are not cherished in Wang Lung's time and culture because they do not serve to increase the prosperity of the family. When the family is on the brink of starvation, O-lan wants to sell their daughter as a slave to get money to feed the rest of the family. She does not see this as a horrible fate because she herself was sold as a slave to the House of Hwang when she was a young girl. She accepts this as the reality of the times. Wang Lung, however, feels guilty about not being able to support his family and refuses to sell the girl away into an unknown future. He yells out of frustration because fate has dealt him this reality.
Even though he is delighted with his first son, having too much happiness and fortune isnt a good thing. "...malignant spirits throughout the air cannot endure the happiness of mortals." It will cause the evil spirits to become involved resulting in misfortune. This is why he screams it is a girl and while walking back with O-lan, after displaying the baby to the House of Hwang, wished that she is dead.