In predictions, this question often comes up: Can I marry him (or her)? Do we have a connection? In fact, no predictor can tell from the Ba Zi whether this particular set of characters represents a person who will marry Zhang San or Li Si. At most, they can describe some characteristics of the other person. When faced with such questions, the compatibility of the two people's Ba Zi marriage information can be used as a reference. If the years when both of them have good fortune are the same, and the years when they face difficulties are also the same, then they are considered to have a connection. If the information is very inconsistent, they are considered to have no connection at all. The situation of extramarital affairs should also be judged based on this principle.
Traditional methods for matching Ba Zi in ancient times:
First, the zodiac animal method, which uses the relationship between the male and female's year branches to determine compatibility. It is said that if the year branches are harmful to the marriage, they are not suitable; if they clash or are in conflict, they are also not suitable.
Second, the year pillar method, which looks at the relationship between the two characters of the year pillar to determine whether the marriage of a man and woman is auspicious or not. If there is a heavenly harmony and earthly harmony in the year pillar, the marriage is auspicious; if they are compatible, it is also auspicious. If there is a heavenly clash and earthly conflict, it is ominous; if they are in mutual destruction, it is also bad.
Fourth, the use of the "useful deity" method. This means that if the useful deities of the man and woman's Ba Zi complement each other, the marriage is auspicious; if they clash, it is ominous.
Third, the method of divine evils (Shen Sha). This refers to the so-called divine evils present in the Ba Zi. If a man's Ba Zi contains a certain divine evil that is harmful to his wife, he is not suitable to marry a woman. Similarly, if a woman's Ba Zi contains a certain evil that is harmful to her husband, a man should not marry her. This method of marriage compatibility is now almost extinct except in a few rural areas.

In the past, before getting married, parents would take both sides' Ba Zi to a temple for compatibility checking. If the Ba Zi were incompatible, the parents usually did not allow the couple to marry. Because in the eyes of the ancients, incompatible Ba Zi would lead to an unhappy marriage.
The Ba Zi consists of four pillars: the year pillar represents the early life and also the relationship with the grandparents; the month pillar represents youth and the relationship with the parents; the day pillar represents middle age and is also the marital palace, representing the interaction between the individual and their spouse; the hour pillar reflects late life and the relationship with children.
Matching the Ba Zi means looking at the relationships of the Five Elements (Wuxing) between the four pillars of the man and the woman. If there is a clear mutual destruction relationship in the four pillars, regardless of where it occurs, it is not beneficial to either the man's or the woman's family. The parents would consider these issues: first, fear of being harmed themselves; second, fear of harming the children's future career; third, fear of harming the grandchildren, leading to misfortune or early death of the descendants. Therefore, people with incompatible Ba Zi typically do not get married.
In modern terms, "incompatible Ba Zi" is a metaphorical expression, indicating that the two people have different views on life and the world. This is different from the original meaning of "incompatible Ba Zi." If two people always have disagreements, their life together will not be happy or fulfilling.