Why did Yuan Tiangang reveal the secret when he knew it couldn't be revealed?

Knowing that the cat is unbreakable, Yuan Tiangang exposed the cat, not voluntarily, but I don't know how it came out.

Yuan Tiangang was a metaphysician and astronomer in the late Sui and early Tang Dynasties. It is said that he is good at "Feng Jian", that is, he can judge good or bad according to the wind and direction. And he is proficient in fortune telling and divination. It was an official order in the Sui Dynasty and was later established in the Tang Dynasty. When Emperor Taizong heard about his deeds, he was admitted to the imperial court as a think tank. ?

According to legend, Yuan Tiangang once visited the Wu family. Yuan Tiangang met Wu Zetian's mother, Yang, and said? When should your wife give birth? . Yang also knows that Yuan Tiangang is good at reading fortune. At that time, she had four children. I don't know which one Yuan Tiangang was talking about. So she called Wu Zetian's two brothers. Yuan Tiangang shook his head and said that although his son was rich and powerful, he was not an official at that time. Mother Yang is also called Sister Wu Zetian, but Yuan Tiangang still shook her head and said that Miss Yang is rich, but she is also a husband, so I'm afraid it won't end well. Finally, Wu Zetian, who was still in infancy, was left behind. Mother Yang went out with Wu Zetian, and Yuan Tiangang was very surprised to see her. Long eyebrows and phoenix eyes, if you are a woman, when you have a son of heaven? . This statement can scare Wu Zetian's mother. Is the son of heaven something that ordinary people can get their hands on? If it leaks out, it must be a capital crime.

Later, Yuan Tiangang observed the night sky and speculated that Li Jiangshan would meet after the third generation. Wu Dai Tang? I don't know how this prophecy reached the ears of ordinary people, but it was also compiled into a jingle and spread everywhere. This warning soon reached the ears of Li Shimin, and Li Shimin could not sit still. Li immediately called him and asked him: the emperor handed down three generations, the Wu Dynasty. Is this serious? ? Li immediately divined and calculated after hearing it. As a result, Li guessed the same result and concluded that this Wu Shi was in the harem. At that time, Wu Zetian was a talent officially granted by Li Shimin. However, Li did not suggest killing Wu Shi, because it was an act of god. If Li Shimin kills Wu Shi, the country of Li Tang will end in the third generation. If he doesn't kill Wu Shi, Wu Shi can inherit the inheritance of Datang for 300 years, and after Wu Shi's death, Jiangshan will return to Li's hands. After some consideration, Li Shimin decided to let Wu Zetian go.

In fact, Yuan Tiangang revealed that he hoped the son of heaven Li Shimin would make a choice.