Although Duke Ai was the nominal ruler of the state of Lu, his power was so limited that he did not have much choice but to tell Confucius to talk to the Three Families about taking action against the murderer of Duke Jian of Qi.
It was not as if Duke Ai had an army to call into action in any case, even if he had wanted to, because control of that had long been ceded to the Ji, Meng, and Sun clans. Neither did he have any money to fund a new military force because tax collection was also under the management of the very same families, who allowed him barely enough income to maintain his estates let alone embark on any risky adventures.
Although he attempted to break free of the shackles the Three Families kept him in, Duke Ai had neither the means nor the charisma to succeed. In 468 BCE, just over ten years after the death of Confucius, the struggle for power between the duke and the Three Families came to a head when he made an appeal to the rulers of other Zhou dynasty states to come his aid. When none of them answered his call, the duke fled the state to Wei, Zou, and finally the rising southern power Yue. Although he was invited back to Lu later, it was by no means a triumphant return and he spent his final years away from court living in a mansion owned by a family called Shan.
Even though Duke Ai was fulsome in his praise for Confucius after the sage’s passing, he does not appear to have taken his advice too seriously when he was alive. Perhaps, given the constant pressure he was under from the Three Families, the duke had more pressing issues on his mind. It is surely no accident that his posthumous name literally means Duke Sadness.