This custom originates from the legend of Mỵ Châu - Trọng Thủy. Because Trọng Thủy's son-in-law cheated on Princess Mỵ Châu, the people of Cổ Loa have a bad impression of son-in-law.

Besides, Vietnamese people also have a saying "Daughter-in-law are our true children, son-in-law are just our guests" to emphasize the important role of the daughter-in-law. Daughter-in-law is "bought" by her parents-in-law (Daughter is someone's child; Daughter-in-law is bought by parents) and "daughter-in-law has to take care of all the affairs of the husband's family", so she has a important position in the family. In addition, there is another explanation, that it is noticed that after the girls from other places come to be brides in Cổ Loa, they become more beautiful (due to the care of the husband's family), while the girls of Cổ Loa gets married elsewhere (known as "walking through the three ramparts"), her fate is not good (?). This custom no longer exists today.