Sister-in-law always likes to show off in front of us, pretending to be rich, ignoring people and being arrogant. Actually, her family is very poor. Why is this?

I think your sister-in-law is vain and likes to compare with others. This kind of psychology is worshipful and unrealistic. Another point is that there is something wrong with your sister-in-law's cultivation quality. Even though she is rich, she should not be too arrogant to care about others. I think her mind is empty-out of stock, and the family environment of your sister-in-law's parents. Look at your sister-in-law. I don't think her parents have set an example.