Guo Ziyi, the Tang general who put down the An Lushan rebellion, is the story here. He spent decades on campaign under several emperors, was named Prince of Fenyang for his services, and died in 781 in his mid-eighties, one of the few great commanders in Chinese history to outlive his own success with his name and family intact. The rapids in the poem stand for the danger such a career carried, since a general too strong could be destroyed by his own court. Guo survived by steadiness, which is what the poem asks of you while the water is high. The middle grade holds both sides: the current is real, and so is the safe landing for anyone patient enough to wait.