What does it mean that men don't sing birds and heroes don't stop dragons and tigers from singing?

I also like this sentence very much. Let me talk about my understanding: "People don't sing birds". Men should do something, don't chirp like birds; "Heroes don't stop dragons and tigers from singing", although they are heroes, they don't stop dragons and tigers from singing, which means that no matter how strong a person is, don't fight against dragons and tigers that he can't beat, that is, people should assess the situation. Combined with the analysis of the Secret History of Princess Taiping, this sentence was said by Shangguan Waner to Xiang Wangdan. At that time, Li Xiangang was the emperor, and Wan'er wanted to warn Dan to be ambitious, not to be inferior to others, and not to be a bird. But you can't offend Li Xian when his power is in full swing, including robbing Shangguan Zhao Yi himself.