Yang Jian served as the regent for the last emperor of the Northern Zhou Dynasty (557-581 AD). His wife counseled him: "The Northern Zhou is on its last legs. Your position is like riding a tiger—dismounting would be perilous. You have no choice but to press on." Yang Jian found her advice sound. He later founded the Sui Dynasty and reunified China.
This idiom serves as a metaphor for being trapped in a difficult situation where one must continue on a risky course of action, as stopping would be even more dangerous.