How did Jiang Ziya become Zhou Wenwang's counselor?

At the age of 72, Jiang Ziya fished in Panxi (now Baoji, Shaanxi) on the bank of Weihe River, and asked for an audience with Ji Chang. Before hunting, Ji Chang divined a divination and said, "The prey is neither a dragon nor a thorn, nor a tiger nor a bear; The income is the assistant minister who has achieved the hegemony. " Ji Chang went hunting and met Jiang Ziya on the north bank of Weihe River. After talking with Jiang Ziya, Ji Chang was overjoyed and thought that Jiang Taigong was a wizard. He said: "Since our country's great-grandfather said,' A saint will come to Zhou, and Zhou will flourish.' Is that you? We have been expecting you for a long time. Therefore, Jiang Ziya was called "King Tai Gong", and they rode home together, honoring them as surnames.