High forehead refers to a high hairline, which is closer to the top of the head, making the forehead appear wider and larger in area. When I was young, I often heard elders say that a higher forehead is good for one's face shape. I don't know if it's because many important people have high foreheads, but there is also a folk saying that one's future can be predicted by looking at the forehead. As for which school of physiognomy this theory comes from, I didn't investigate deeply, just took it as a joke.

A woman with a very high and broad forehead has strong ambition and a strong sense of career. Unless your forehead is higher than hers or you are willing to be under her leadership, she is not suitable for you to marry.