Why in ancient times, every time a vision was born, it was said that a great man was born?

The emperor always needs a spiritual sustenance, thinking that this is a son with both civil and military skills, and naturally he will love his son more. The representative of this is Emperor Gaozu Liu Bang. According to historical records, Liu Bang's mother often had some bizarre dreams when she was pregnant with Liu Bang, which was very wonderful. As a result, Liu Bang did make great achievements and became the founding emperor of the Han Dynasty.