Has the Li Shimin government made any major mistakes?

Li Shimin was an enlightened emperor with great achievements in ancient China. During his reign, the society was stable and the country was strong, which was called "the rule of Zhenguan" in history. But in his later years, he was uncharacteristic, trusting the alchemist's words and indulging in divination and pills.

In the 21st year of Zhenguan (647), Li Shimin was paralyzed by a stroke. At this time, he began to swallow the alchemy medicine refined by the alchemist, hoping that he would live forever. He ate the Dan medicine refined by the local alchemist first, but it didn't work. He thought that domestic alchemists were shallow in Taoism, so he sent people to visit foreign experts everywhere. In the 22nd year of Zhenguan (648), Wang Xuance, the minister, presented the wife of the captured alchemist Rona to Li Shimin. This man pretends to be 200 years old, has the secret of immortality, and can even make people fly to heaven to become immortals. Li Shimin was convinced of this, and he respectfully reserved a special place for him to refine the elixir of life. A year later, when the medicine was finished, Li Shimin took it gladly. Unexpectedly, there was a severe poisoning reaction soon, and he died of sudden illness due to bleeding. Li Shimin was only 52 years old, and he was the first emperor to die of Dan medicine in the Tang Dynasty.

The most ridiculous thing is that after the emperor died, ministers didn't know how to deal with Rona's wife's insomnia.

After Li Shimin's death, his descendants probably learned some lessons, and for a long time they dared not take the highly toxic Dan medicine. It was not until 170 years later that Tang Xianzong Chunli, who forgot the lessons of his ancestors, became the second emperor to take Dan medicine for poisoning.