Why did an-mei's grandmother say bad things about her own grandchildren?

An-Mei's grandmother likely said bad things about her grandchildren as a way to protect them from bad luck or harm, as seen in Amy Tan's novel "The Joy Luck Club." In Chinese culture, it is believed that by speaking negatively about something or someone, you can prevent misfortune or evil spirits from harming them. By saying bad things about her own grandchildren, An-Mei's grandmother may have been trying to ward off any potential harm or bring about good luck for them.