In his previous life, he was the director of the psychiatry department, but when he opened his eyes, he became the most insane emperor in history.
His elder brother regarded him as a thorn in his side, his father regarded him as dispensable, and everyone in the court was waiting for him to make a fool of himself. He's not crazy. He used the battlefield as a clinic and used people's hearts as medicine. He said that Yu Wentai had a paranoid personality, and that Rouran Khan was manic, depressive, and unruly, and even his eldest brother was "questioned" by him in person.
Everyone thought he was talking nonsense.
It wasn't until he revealed the hidden secrets of his political opponents and subdued tens of thousands of troops without a single blow that everyone was horrified to discover that this "madman" had already seen through all their thoughts.