What did mother mean when she warned, "how we act today foretells the whole year"?

It is the Vietnamese New Year, February 11, Tet 1975, the Year of the Cat. When we first meer Ha and her family, they are celebrating. In this chapter, Ha’s mother explains how each person behaves this day will foretell the entire year. Ha is jealous since only men can rise first in order to bring luck to the house.

In this section, we learn Ha's family is traditional. They celebrate Tet, and they adhere to traditional customs such as men having to walk around the house first to bring good luck in the New Year, and they visit a fortune teller who will predict the coming year for the family. Note, many Vietnamese, including Ha’s mother, take the advice of the fortune teller seriously. It isn't accidental or cultural aside that the fortune teller is included in this section of the novel. The fortune teller’s warning that things will be difficult for Ha and her family should not be taken lightly. Instead, the fortune serves as an ill-omen for things to come.